Ecophysiology of Five Subalpine Acaena Species in Relation to Habitat

ECOPHYSIOLOGY OF FIVE SUBALPINE ACAENA SPEC! IN RELATION TO HABITAT

A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Botany in the University of Canterbury

L. N. CONNER ?

1981 "In the case of every species, many different checks,

acting at different periods of life, and during different

seasons or years, probably come into plaYi some one check

or some few being generally the most I but all

concurring in determining the average number or even the

existence of the species".

- Darwin (1859, p.125) i

CONTENTS

PAGE

LIS'l' OF FIGURES v

LIST OF TABLES vi

LIST OF PLATES viii

ABBREVIATIONS ix

ABSTRACT 1

CHAPTER

1 INTRODUCTION 2

1.1 GENERAL INTRODUCTION 2

1.2 OBJECTIVES 3

2. THE SPECIES AND THEIR HABITATS 5

2.1 THE SPECIES 5

2.2 HABITATS Itr

2.2.1 Distributions of the species l~

2.2.2 Description of study area 15

2.2.3 Vegetation sampling 20

2.2.4 ion analysis 22

2.3 RELATIONSHIPS WITH OTHER ORGANISMS 32

2.3.1 Mycorrhiza 32

2.3.2 Herbivores 32

2.3.3 Pathogens 35 ii

PAGE

CHAPTER

3 SEED ECOLOGY OF ACAENA 36

3.1 INTRODUCTION 36

3.2 MORPHOLOGICAL ADAPTATIONS FOR DISPERSAL 36

3.3 FACTORS CONTROLLING GERMINATION 37

3.3.1 Introduction 37

3.3.2 Materials and methods 39

3.3.3 Results and s 42

Seed viability 42

response 43

Response to cold storage 43

Response to light 43

The effect of water availability 47

to GA and kinetin 47 3

Response to KN0 47 3 The effect of ethanol and HCl 50

Additional experiments relating to A. inermis 50

3.3.4 Discussion 52

4 COMPARATIVE RESPONSES TO WATER STRESS 56

4.1 INTRODUCTION 56

4.2 MATERIALS AND METHODS 59

4.2.1 Growth response in different water regimes 59

4.2.2 to water loss from exised leaves 60

4.2.3 Examination of micromorphological charact eristics 60

4.3 RESULTS AND ANALYSIS 61

4.3.1 Growth response in different water regimes 61 iii

CHAPTER PAGE

4.3.2 Response to water ~oss from exised leaves 63

4.3.3 Micromorphological characteristics 70

4.4 DISCUSSION 78

GROWTH IN RESPONSE TO SOIL QUALITY AND NUTRIENT SUPPLY 82

5.1 INTRODUCTION 82

5.2 MATERIALS AND METHODS 83

5.2.1 Rooting of cuttings 83

5.2.2 Growth on different soils 84

5.2.3 Growth in relation to soil fertili~y 84

5.2.4 Relative growth rates 87

5.3 RESULTS AND ANALYSIS 89

5.3.1 Growth on different soils 89

5.3.2 Growth in response to soil fertility 92

5.3.3 Growth rate 97

5.4 DISCUSSION 98

6 INTERFERENCE RESPONSES ON THREE SOIL TYPES 102

6.1 INTRODUCTION 102

6.2 MATERIALS AND METHODS 105

6.3 RESULTS AND ANALYSIS 106

6.4 DISCUSSION 115

6.4.1 Mutual stimulation 115

6.4.2 Mutual depression 116

6.4.3 Compensating increases and decreases 116

6.4.4 Comments on the experimental approach 117 iv

CHAPTER PAGE

7 CONCLUDING DISCUSSION 119

Adaptations t.o the environment 119

Factors 1 the distributions of each species 121

ACKNOWLEDGEMENTS 125

REFERENCES 126

APPENDIX I 136

APPENDIX II 144

APPENDIX III 146 v

LIST OF FIGURES

FIGURE PAGE

2.1 Acaena caesiiglauca 7

2.2 Acaena fissistipula

2.3 Aqaena glabra 10

2.4 Acaena inermis 11

2.5 Acaena profundeincisa 13

2.6 Location of study areas 16

2.7 Location of Porters Pass and environs 17

2.8 Ordination of species 24

2 0.9 Ordination of sites 26

3.1 Effect of temperature on germination 44

3.2 Effect of light on germination 45 -4 -3 3.3 Effect of 10 M and 10 M gibberellic acid (GA ) 3 on germination 48

3.4 Effect of 10-4M and 10-3M kinetin on germination 49

3.5 Effect of 50% ethanol and 10% Hel on germination 51

4.1 Relative water contents and rates of relative water loss from excised leaves 64

5.1 Vertical section through a seedling container 88

5.2 Growth of Acaena on natural soils in response to nutrient addition 94

5.3 Growth of Agrostis tenuis on natural soils In response to nutrient addition 96 vi

LIST OF TABLES

TABLE PAGE

2.1 Particle size analysis and water holding capacity of three soils from Porters Pass 21

2.2 The presence o~ Acaena species in site types 28

3.1 Effect of storage on seed viability 42

3.2 Effect of constant and alternating temperatures on germination 46 o 3.3 Effect of cold storage (-25 C) for 1 and 2 months on germination 46

3.4 The influence of water availability on germination 4 I

3.5 Effect of 2% (w/v) KN0 on germination 3 50

3.6 The germination response of A. caesiiglauca~ A. fissistipu and A. glabra after 50 days and tomato, radish and carrot after 6 days, when treated with A. inermis seed leachate 52

4.1 Treatment means and ANOVA for growth of five Acaena species in different soil water tensions after 5 weeks 62

4.2 Relative water content at stomatal closure and ANOVA 69

4.3 Rate of increase in water loss and ANOVA (a) prior to stomatal closure (corrected for cuticular loss) and (b) after stomatal closure 70

4.4 Stomatal indicies and ANOVA 72

4.5 The number of epidermal cells per unit area and ANOVA 73

5.1 The composition of mineral nutrient treatments 86

5.2 (a) Mean growth on natural soils and potting mix of cuttings from Arnuri and Porters Pass (b) ANOVA 90

5.3 ANOVA of growth of the five Acaena species in response to nutrient treatment on three natural soils 93

5.4 ANOVA of growth of Agrostis tenuis in response to nutrient treatment on three natural soils 95 vii

TABLE PAGE

5.5 Mean relative growth rates and ANOVA 97

6.1 Sums and differences of Acaena species in all combinations, and with Agrostis ten:uis~ Rumex acetosella and Trifolium repens when grown on (a) coarse gravel (b) fine gravel and (c) yellow brown earth 107

6.2 Analysis of between and within mixed culture pots and between monoculture pots when Acaena are grown with 'one another and (a) Agrostis tenuis (b) Rumex acetosella and (c) Trifolium repens 109

6.3 Mean differences between mixed and monoculture yields/half pot 112 viii

LIST OF PLA'rES

PLATE PAGE

2.1 study site at Porters Pass 18

2.2 A. caesiiglauca in a habitat 29

2.3 A. fissistipula in a streamside habitat 29

2.4 A. glabra in a scree habitat 30

2.5 A. inermis on coarse gravel 30

2.6 A. profundeincisa in a habitat 31

2.7 Endomycorrhiza 33

4.1 Scanning electron micrographs of leaf surface) wax structures 74

4.2 Scanning electron micrographs of leaf (abaxial surface) wax structures 76 ix

LIST OF ABBREVIATIONS

n number of replicates v/v volume/volume w/v weight/volume

ANOVA analysis of variance df degrees of freedom

MS mean square

F variance ratio s ns not s t test = student's t test t' test= Cochran's of the Behrens-Fisher test

(the approximate t test) . Used where

of sample variances is too great to meet the ions

of the standard t test. 2 X Ghi--square

L.S.D. least difference (Sokal and Rohlf 1969, p.235).

* p < 0.05 * * p < 0.01 * * * p < 0.001

Different lower case letters after mean or mean ± standard deviation denote values significantly different (p < 0.05) based on Duncan's new range test. I

ABSTRACT

.The ecophysiology of five subalpine Acaena species: A. caesiiglauca~

A. fissistipula~ A. glabra~ A. inermis and A. profundeincisa~ was examined

in relation to their habitats at Porters Pass. All five species

A. profundeincisa~ had distinct habitat preferences. Experimental compari-

sons of their seed ecology, adaptations to water stress, growth responses

and interference potential were used to examine how each species is

to its preferred habitat.

A. caesiiglauca has a distinct e for grassland/scrub habitats.

Its absence from drier sites is attributable to its inability to tolerate desiccation. A. fissistipula is restricted to streamside habitats because it is unable to tolerate desiccation. Its low interference potential excludes it from grassland/scrub habitats. A. glabra and A. ine2~is~ due to their poor interference potential, are limited to sites with high evaporating conditions where few other species grow. However they have adapted to these environments in different ways. A. glabra has developed an ext en- sive transpiration system to an efficient cooling It has therefore made a compromise between closing stomata to resist desiccation and maintaining open stomata for continued photosynthesis. In contrast,

A. inermis attempts to minimize water loss by having a low stature with extensive branching to form mats. Its leaves are also more physiologically tolerant of desiccation. A. profundeincisa has no distinct habitat pref~ erence. Optimum germination occurs at a lower temperature than the other

which is reflected by its higher altitudinal distribution. It is relatively tolerant of water stress and has a high interference potential, which enables it to inhabit a variety of habitats. 2

CHAPTER 1

INTRODUCTION

1.1 GENERAL INTRODUCTION

The question "why do plants grow where they do?" is fundamental in plant ecology. The relationships between plant growth, distribu~ion and physical environments need to be known before any understanding of plant communities (particularly interactions within the community and community changes) can be made. The plant environment can be divided into a rnulti- dimensional array of factors grouped according to their sources: climatic, edaphic and biotic, which collectively influence plant growth, morphology and reproduction. Each element within the environmental complex may act or interact, additively or compensatingly, as major controlling factors or only as triggering agents (Billings 1952). Due to the inherent complexity of natural systems, there exist numerous habitats within a community. Such spatial variability allows many species with slightly different requirements and responses to coexist in the same community (Grubb 1977) . There is therefore a need to establish:

(a) the habitat of a species,

(b) how a species is adapted to its habitat and

The various approaches used to investigate the relationship between species and their habitats have been divided into direct, correlative, and comparative types (Grime 1965). The direct and correlative approaches, involving field sampling and environmental monitoring, rely on the assump- tion that species distributions are controlled by specific measurable variables. However the number of environmental variables that can be readily measured are limited and often interact. Furthermore, although changes in environmental variables are oft~n correlated with changes in 3

vegetation, few are the cause of the change. In addition, environmental

variations may be imposed by the plants, rather than the reciprocal. For

these reasons, factor correlations shed no light on the underlying causal

principles and processes determining how each plant succeeds in a particular

set of conditions.

In contrast, the comparative experimental approach allows the examin

ation of individual factors which are considered to be of overriding import-

anceD The use of standardized conditions ensures that differences between

species are occurring with respect to the same variable or group of variables.

Experiments using plants of closely related species further reduce variation

due to plant form and morphology. The comparative approach was therefore

used throughout this study to investigate the ecophysiological responses

of five closely related species.

1.2 OBJECTIVES

The aim of this study was to examine the adaptations which allow some

species of Acaena Linn. (Rosaceae) to inhabit subalpine tussock grassland

communities and to compare their growth requirements and environmental

responses in order to determine the factors which may limit their distributions

in the field. Due to the current taxonomic confusion within the genus

Acaena, the five speoies used in this study (A. caesiigZauca, A. fissistipula,

A. glabra, A. inermis and A. profundeincisa ) are described in Chapter 2.

Their habitats were characterised at two field sites, including a detailed

floristic analysis for populations from Porters Pass to examine whether the

species differed ecologically in their habitat distributions. This led to experimental comparisons between the species so that the relative responses to environmental factors could be assessed, along with their importance in determining the survival and ecological preferences of each species.

Factors which were considered important included the seed ecology of each 4

(Chapter 3), adaptations to water stress (Chapter 4), growth responses (in particular, growth in relation to soil quality, including nutrient requirements and growth rate analysis) (Chapter 5) and responses to interference 6) . The importance of each factor is outlined in the relevant and the overall significance of these responses to each ~pecies is discussed in Chapter 7. 5

CHAPTER 2

THE SPECIES AND THEIR HABITATS

2.1 THE SPECIES

This study is concerned with five Acaena species: A. caesiiglauca~

A. fissistipula 3 A. glabra~ A. inermis and A. profundeincisa~ all of which grow sympatrically in subalpine tussock grassland habitats in the South

Island. The genus belongs to the family Rosaceae, subfamily Rosoideae and is included in the tribe Sanguisorbae. The number of species are estimated to be somewhere between several dozen and a hundred (Dawson 1960), mainly distributed in the southern hemisphere with several es in the northern hemisphere: 1 in California, 1 in Mexico and 1 in Hawaii, as well as a few others which extend across the equator in South America. Other- wise the majority of species are found in South America and New Zealand, with only 3 species in Australia, 1 in south Africa and 3 or 4 in the Ant- arctic circum- polar islands. The taxonomic status of the genus in New

Zealand is currently being revised (Botany Division, D.S.I.R., Lincoln) and

19 entities will be recognised as native to New Zealand. Due to the taxonomic confusion within the genus, descriptions of the species used in this study are given below.

Acaena Linn., Mantissa Plantarum 2: 200 (1771)

Herbaceous to semi-woody perennials with creeping stems l rooting at nodes; leaves alternate, pinnately compound, stipules adnate to petiole; leaflet margins serrate; ascending scapose flowering branchlets; inflor esyence capitate or spicate; flowers usually perfect; cupule usually extended distally into 4 spines or with numerous hooks, sepals usually 4, petals absent, stamens 1-7: s 1 or 2, stigmas plumose. A. caesiigZauca (Bitter) Bergmans Vaste PZ. Rotsheest. ed. 2

1939, 65. A. sanguisorbae Vahl subsp. caesiigZauca Bitter in BibZ. bot.~

Stuttgart 2.!, 1911, 269. (Fig. 2.1).

Main sterns stout, creeping, rooting from nodes; root system deep

and woody in mature plants; stern, scape, petiole and median nerve of the

leaf covered with dense spreading hairs; branches about 5 cm long. Leaves

3.5-5 cm long, 7-11 foliate, stipules lanceolate, entire, sometimes 1-2 fid.

Leaflets blue-grey on both surfaces, appressed silky-pilose on veins and veinlets, more densely so on under surface, serrate, subsessile; lower leaf

lets small, approximately 2 rnrn long, 3-8 toothed; upper leaflets up to 12 mrn long, 8-9 toothed. Scapes densely pilose, up to 16 cm long, with one or more pairs of bracts. Heads globose, up to 2 cm diameter including spines.

Cupules obconic, 4-angled, densely pilose. Spines up to 8 mrn long, brown, barbed. Sepals lanceolate, densely hairy below. Stamens 2, anthers white. Stigma white, plumose.

A. fissistipuZa Bitter in BibZ. bot.~ Stuttgart 2.!, 1911, 247.

(Fig. 2.2).

Main sterns slender, but may become woody, creeping, rooting from the nodes, glabrous; extensive deep woody root system in older plants; branches ascending to spreading, sparsely hairy, up to 5 cm long. Leaves

2.5-10 cm long, 7-11 foliate, stipules leafy, deeply 3-5 fid, teeth linear- lanceolate up to 4 rnrn long with brush~like hairs at the tips. Leaflets glaucescent on both sides, the margin somewhat reddish, serrate-dentate, almost glabrous above, dense appressed hairs on the veins below; teeth penicillate. Lower leaflets 3fid, 1-2 mrn long, becoming gradually larger along leaf; upper leaflets orbicular or wider, terminal leaflets up to

10 x 10 mrn on petiolules 3-5.mrn long. Scapes up to 22 cm long, with or without one or more pairs of bracts, almost glabrous to densely pilose, slightly reddish. Heads globose, 1-2 cm diameter including spines, 7

Figure 2.1 A. laucaa. habit (xl) b. leaf (xl) c. seed (x8). 8

Figure 2.2 A. fissistipuZa a.habit (xl) b.leaf (xl) c.seed (x8). bract lets linear, c Cupules approximately 1 mm long,

densely pilose; spines 4, 3-5 mm long, red-brown with barbed tips.

s broadly lanceolate, below, green, often red tinged.

Stamens 2, anthers purple. Stigma red, plumose.

A. glabra Buchan. in T.N.Z.I.'1.J 1872,?26,t.14. (Fig. 2.3).

Perfectly glabrous herb; main stems creeping and rooting, up to

50 cm long. Branches more erect and than the other species

described in this study, up to 10 cm long, stout and woody. Roots long,

woody. Leaves up to 5 cm long, coriaceous; up to 1 em long, 3-5

fid; leaflets 7-11, cuneate at the base, divided into 5-8 obtuse

teeth, upper pair up to 1 cm long, pale , often tinged with

red , shinning above, subglaucous below. erect glabrous,

up to 13 cm long, usually naked, sometimes with one or two pairs of bracts.

Heads , up to 1.5 cm diameter, greenish to reddish, bracts linear,

ciliate. Cupules approximately 4x5 mm , compressed, 4-winged, two lateral wings Spines 4, up to 2 mm long but sometimes vestigial,

broad-obovate, with dark red margins towards end of season.

Stamens 2, anthers white, filaments long. Stigma fimbriate.

A. inermis Hook. f. Fl. N.Z. !, 1852, 54. A. microphylla var. ine:r>mis (Hook. f.) Kirk Stud. FI. 1899, 134. A. microphyUa var.

Allan FI,N.Z. 1, 1961, 357. (Fig. 2.4).

From the author's observations and taxonomic comparisons made by

B. M. MacMillan, (Botany Division, D.S.I.R., Lincoln), A. inermis, as described by Hooker in 1852 and A. microphyUa var. robusta (Allan 1961) are considered to be the same , the specimens only differing with respect to the development of spines. In this species, spines develop after anthesis and are often only partially developed before the onset of winter or may not develop at all. Both 'spined' and 'unspined' forms occur 10

Figure 2.3 A. glabra a. habit (xl) b. leaf (xl)

c. seed (x8). 11

Figure 2.4 A. inermis a. habit of form (xl) b. head (xl) c. seed (x8) d. seed (x8) e. leaf (xl) 12

together, occasionally on the same plant and cannot be distinguished prior

to the development of spines. These forms are considered synonomous in

this study.

Main stems robust, woody, much branched, creeping and rooting, form-

ing extensive mats. Branches ascending, slender, short, up to 10 cm long,

glabrous to sparsely hairy. Leaves narrow, obovate, up to 7 cm long, 11-17

foliate, stipules 2 fid. Leaflets crenate, purplish to olive or bronze~

green above, subglaucous below, sessile. Upper leaflets approximately 5 rom

long, glabous above, pilose on veins below, suborbicular, subs€ssile, teeth

penicillatei terminal leaflet about 3 rom long with petiolule up to 3 mm.

Scapes up to 3 cm long, glabrose to pilose, sometimes with a pair of bracts.

Heads globose, up to 3 cm diameter including spines; bractlets linear, two

toothed at apex. Cupules 2-3 mm , turbinate, glabrous, 4-angled,

sometimes spined, when present up to 1 cm long, crimson to brownish-red,

unarmed. Sepals ovate, dull green to brown. Stamens 2, anthers white to

creamy. Styles 2, fimbriate on one side. Achenes 2, usually only 1

developed.

A. profundeincisa Bitter in Bibl. bot.~ Stuttgart 1911, 270.

(Fig. 2.5).

Main stems slender, creeping and rooting, woody; roots deep, woody;

branches ascending or spreading, up to 10 cm long, pilose. Leaves 4.5-8 cm

long with 11-13 leaflets, petioles pilose; stipules leafy, lanceolate,

entire or deeply 1-2 fid; leaflets 9-11, acutely toothed; upper leaflets

6-8 rom long, serrate, with seldom more than 9 teeth, broadly oblong to

obovate-oblong; green above, subglaucous below with appressed silky hairs,

especially on the veins and margins, short hairs on upper surface. Scapes

up to 13 cm long, pilose, brown to slightly reddish, with or without one or more pairs of bracts. Heads globose, 9-17 rnm diameter including spines, 13

Figure 2.5 A. profundeincisa a. habit (xl) b. seed (xB) c. leaf (xl). 14-

bractlets linear, ciliate, pilose; cupule 3-4 rom long, densely pilose;

spines 4, 5-7 rom long, green to pale reddish with barbed Sepals

ovate, often tinged with red, pilose below. Stamens 2, anthers red;

stigma plumose on margin, becoming reddish in the middle.

2.2 HABITATS

2.2.1 Distribution of the s

The following distribut,ions of the five Acaena species are based on

herbarium specimens and collections made by Ms. B. M. MacMillan (Botany

Division, D.S.I.R., Lincoln).

Acaena caesiigZauca is widespread east of the main divide in the

South Island. It occurs in montane and subalpine grassland and/or open ground with an upper altitudinal limit of approximately 1,200 m a.s.l.,

Acaena fissistipuZa is widespread in the South Island, especially east of the main divide and in the Central Otago mountains. It occurs in montane to subalpine grassland in moist places and under light shade.

Acaena gZabra is rare to locally abundant in the South Island from inland Marlborough and the Seaward Kaikoura mountains to inland Canterbury as far south as the Torlesse Range. Its habitat is restricted to montane and subalpine screes, streqrnbeds and rocky places.

Acaena inermis 1S widespread in the South Island especially east of the main divide. It is also known from the Northern and Eastern Ruahlne

P~nges and the volcanic plateau in the North Island. It occurs in montane to subalpine open sites on shingle or riverbeds.

Acaena profundeincisa is rare to locally abundant in subalpine to alpine tussock grassland predominantly east of the main divide and the Otago mountains in the South Island, where the known lower altitudinal limit is 15

approximately 940 m a.s.l .. It is restricted to an alpine distribution

in the North Island up to approximately 1,700 m a.s.l .•

2.2.2 Description of study area

The main study area was at Porters Pass (S74 215853) although some observations were made at Amuri Basin (S47 897109) (see Fig. 2.6). The

Porters Pass site was chosen because all five Acaena species grow there and

it was readily accessible via the main West Coast Road.

The history, climate, soils and vegetation of Porters Pass have been described by Molloy (1963, 1964). The Pass is formed from a natural topographical gap separating the Big Ben and Torlesse Ranges. The gully so formed, Starvation Gully, provides a passage between the Big Ben

Range and the southern end of the Craigieburn through which hot, dry nor-westerly and south-westerly air streams bearing precipitation are channelled (see Fig. 2.7).

Periodic erosion of the Kaikoura steepland soils is a prominent

feature of the area. At higher altitudes t screes predominate with differ- ential movement along the borders of mobile tongues. Some specialized plants maintain a precarious existence on the semi-mobile with others invading as stability increases towards the margins. At lower altitudes on gentle inclines, the vegetation is dominated by Dracophyllum scrub

(Dracophyllum acerosum) and depleted snow-tussock, Chionochloa m~cra, grassland.

This study was concentrated on the south-west slopes of Foggy Peak

Ridge where two V-shaped lies channel water into streams that drain into

Lake Lyndon and ultimately into the Rakaia River. These slopes have remarkably shallow soils, extensive soil erosion and appressed, wind shorn vegetation (Plate 2.1). 16

q .... .100 km.

Figure 2.6 Location of study areas. 17

o 1 2 km.

2.7 Location of Porters Pass and environs. 8

Plate 2.1 Study site at Porters Pass. 19

No permanent climate recording stations are located close to the

Pass, the closest full recording compliment being situated at Lake Coler

approximately 20 km south-west in the Rakaia River catchment (N.Z. Meteor-

ological Service 1973). However temporary climqtological data has been

recorded for Foggy Peak Ridge (Molloy 1963) and for the Kowai Stream catchment (Hayward 1980) approximately 2 km east of Porters Pass.

The climate is considered to be cool (Molloy 1963) with heavy snow

falls during June, July and August. Snow may accumulate up to two metres in depth and lie for several weeks on end. This would protect the vegetation from desiccating winds and prevent excessive freeze-thaw effects on the soils. In addition, it provides a source of moisture upon sublimation in the spring. When winds predominate, low cloud, mists and are frequent (Molloy 1963) resulting in reduced light intensities and increased humidity. In spite of a great number of cloudy days, there are many periods of brilliant sunshine with intense solar radiation.

Although annual precipitation is probably ample for plant growth (approximately 1500 mm, Hayward (1980» periodic water deficits would be experienced on more exposed sites during summer, when frequent desiccating north-westerly winds reach high velocities. Shallow, well drained soils with low moisture storage ntial would compound water deficits. Air temperatures (30 crn

0 above ground) range from -lOoC in July to 29 C in November, whereas soil o . temperatures (45 em below ground level) range annually from 0-15 C (Molloy

1963) .

Soils are formed from lower Mesozoic greywackes and ites of the New Zealand Geosyncline and belong to the Kaikoura steepland set (N.Z.

Soil Bureau 1968). They are weakly weathered but strongly leached with poor reserves of essential plant nutrients, especially nitrogen, phosphorus and sulphur (Williams et aZ. 1978). Due to periodic erosion, there is a 20

wide range in the age of soils from different sites. On the uppermost

sites used in this study (approximately 1010 m) there are large, super-

ficially weathered blocks of and argillite suspended in a matrix of smaller angular fragments, sands and silts. This represents the soil of most recent origin (coarse gravel). Deposits beneath DracophyZlum scrub-

Chionochloa tussock grassland are yellowish in colour, changing gradually to a brighter yellow with decreasing altitude (yellow brown

Some of these older soils have been completely buried by erosion products from soils upslope, the development of which provides a third soil type near the summit of the Pass (fine gravel).

Samples of these three soil (top 10 cm) were collected so ~hat they could be used for experimental purposes. The size distribution and the water holding capacity of each soil type is given in Table 2.1.

All three soil can be classified as silt loams (Taylor and

Pohlen 1962, p:S5) with and are light, loose and porous but very susceptible to frost action (Gradwell 1960). Coarse has a larger proportion of fine sand (0.02-0.2 mm) and a lower clay content than the other soils, indicating a more recent Yellow brown earth has the highest water holding capacity followed by fine gravel and coarse gravel.

This trend is a reflection of the relative stoniness of the soils.

2.2.3

The vegetation at Porters Pass was sampled quantitatively so that the species with which the Acaena species are associated could be deter mined and the habitat preferences, if any, of each Acaena species could be assessed. The greatest abundance of the five Acaena species was observed to follow the two V-shaped gullies (Plate 2.1). Statified ing of these gullies and some erosion slips and screes, was carried out by placing quadrats at random along lines (30) across the gullies. The abund- TABLE 2.1 PARTICLE SIZE ANALYSIS AND WATER HOLDING CAPACITY OF THREE SOILS FROM PORTERS PASS. MEAN ± STANDARD

n=4, METHODOLOGY FOLLOWED N.Z. SOIL BUREAU (1968) PART 3 1 p.5).

Stones > 2 rom Water Holding % Coarse Sand % Fine Sand % Silt % Clay Textural (% of Initial Capacity Soil G. 0.2-2 rom 0.02-0.2 rom 0.002-0.02 rom <0.002 Class Sampler (% vol.) I

Coarse gravel 14.00 ± 2.58 41.50 ± 3.32 28.50 ± 1.91 16.00 ± 0.82 Silt Loam 86.25 ::!: 6.99 1. 67 0.71

Fine gravel 29.25 ± 11.32 21.00 ± 3.87 37.25 ± 5.38 21.50 ± 1.91 Silt Loam 55.75 ± 4.92 8.00 ± 2.12 I

Yellow brown 33.50 ± 8.27 26.25 ± 4.57 23.00 ± 2.45 17.25 ± 1.71 Silt Loam 27.25 ± 5.85 34.67 ± 3.54 earth

ex. n=3

10 I-' 22

ance was estimated (to the nearest 5%) for all species in a total 2 of 152 1m quadrats. When a species covered less than 5% of a quadrat,

it was scored as "+" so that its presence was recorded. All species of

non-vascular plants were grouped as mosses, lichens and liverworts. Each

quadrat was assigned one of three site-type categories: streamside, sCree or grassland/scrub. Streamside sites and screes had predominantly coarse

gravel soil/whereas grassland/scrub sites occurred on yellow brown earth.

A. inermis was not as abundant in the sampled gullies as the other four

species but was more frequent in open sites on fine gravel soils nearer the summit of the Pass.

2.2.4 is

Of the available ordination methods used to describe the composition of vegetation, Principal Components Analysis and Reciprocal Averaging techniques seem to be the most suitable (Gauch et at. 1977). The ective of both techniques is to extract axes which define the underlying structure of the relationships among species and the relationships between vegetation and habitat variation. Ordinations resulting from the Reciprocal Averaging method, as outlined by Hill (1973), were found to be more suitable for describing the vegetation and habitat relationships at Porters Pass, probably because of the diverse nature of the sample set. It is well known that many of ordination such as Princ Components Analysis are increas- ingly distorted with increasing diversity among samples. This is attributed to the ecologically inappropriate assumptions that relationships between vegetation and the environment are linear (Gauch and Whittaker 1972, Gauch et at. 1977) and that var conform to normal and homogeneity

1980) . Reciprocal Averaging appears to be more tolerant of sample diversity because it employs a simultaneous double standardization of the primary data matrix and Chi-square (rather than covariance or correlation) distances

(Noy-Meir and Whittaker 1977) . Therefore only ordinations using the Recip- 23

rocal Averaging technique are presented. A copy of the program designed

by Hill (1973) was obtained from Dr. N. D. Mitchell (Auckland University).

Only the most abundant species (those in at least 10 quadrats) were used in

the analysis. The data used are given in Appendix I.

The species ordination (Fig. 2.8) shows that A. glabra is not closely

associated with any other species used in the analysis. This suggests that

it is a poor competitor and is restricted to sites where the other species

are unlikely to grow. A. fissistipula occurs at the other extreme of axis

2 compared with A. glabra and also has few closely associated species.

A. fissistipula, along with species geometrically close to it (Trifoliwn

repens, Cerastiwn fontanum and lobiwn alsinoides subsp. atriplicifolium> ,

primarily occur in moister areas or where water is abundant. A. inermis is

associated with species which invade depleted grassland such as Rumex ace-

tosella~ Hypochaeris radicata and Hieraciwn lachenalii. A. caesiiglauca

and A. profundeinoisa appear to have the most similar habitat types of the

five Acaena species. A. caesiigZauca is associated with A1uehlenbe,~kia axillaris~mosses and Cyathodes colensoi" whereas A. profundeincisa is most

closely associated with Luzula banksiana var. orina and mosses.

The sites ordination (Fig. 2.9) shows that although there is some

overlap in the imposed site type classification i.e. between streamside,

grassland/scrub and scree sites, the streamside and grassland/scrub sites

appear to be separated to a certain extent by axis 1 and the scree sites by

axis 2.

Assuming that the imposed classification does reflect three different habitats within the community, analysis of the presence of each species in each site type may indicate whether the Acaena species have distinct habitat preferences. A Chi-square analysis on the presence of Acaena species in site (Table 2.2) shows that A. caesiigZauca was found more often in Ax/'S 2 00 24

018

014 033 01 025 f 1fl Ac in 24t:;Q37 o ~ '26 017 220:nf) qz.y 036 Cl32 ~ 023 199 Ac fi 12 OL-~--~~~--~~--~--~~--~~ Ax! 1 100

031

flAc gl °12 016 5 flAc fi 19 013 °8 2() 32 036 014 '%38 alB 35 62 J 034- 0°4- 0011 03 ~08 0'1 2 02~t' 39 6 017 25 on flAeCQ 0 21 018 • Acn • °26 ACfTo 033 15

Figure 2.8 Ordination of species. 25 Axis," 3 to 031

10 o

Ac~ 13 16 o 50 Ac fi 012 19. t9 3;8»> J d8 35~~ 0" ~~~5 Ac ca~ll 11,39 21 01 018 026 o 15 033 8Ac pr O~~~~--~~--~--~----~--~~AXI 2

Ac ca= Acaena caesiiglauca 18 Geranium sessiliflorum Ac fi= Acaena fissistipula 19 Hebe pinguifolia Ac gl= Acaena glabra 20 Helichrysum bellidioides Ac in= Acaena inermis 21 Hieracium lachenalii Ac pr= Acaena profundeincisa 22 Hieracium pilosella 1 Agropyron scabrum 23 Hieraoium praealtum 2 Agrostis tenuis 24 Holcus lanatus 3 Anisotome aromatica. 25 Hypochoeris radioata 4 Anthoxanthum odoratum 26 Luzula banksiana var. orina 5 Blechnum penna-marina 27 MuehZenbeokia axillaris 6 Celmisia spectabilis 28 Ourisia caespitosa 7 Cerastium fontanum 29 Pimelia oreophila 8 Chionochloa macra 30 Poa oookayniana 9 Coprosma depressa 31 Poa ooZensoi 10 Coriaria sarmentosa 32 Podooarpus nivalis 11 Cyathode$ coZensoi 33 Rumex aoetoseZla 12 DracophylLum acerosum 34 Senecio belZidioides 13 DracophylZum pronum 35 Trifolium repens 14 Epilobium alsinoides 36 Viola filioaulis subsp. atripZicifolium 37 Wahlenbergia albomarginata 15 EpiZobium melanocauZon 38 Lichens 16 Festuca cf rubra 39 Mosses 17 Gaultheria crassa 26

Axis2 100 0

o o

o o o

50 o

tJ o o 0 o .,. o

.,. o.L..----=+~_._____.__-_r______.,..____..._-...... ______..____,.____, A xis 1 100

Figure 2.9 Ordination of sites. + streamside o scree • grassland/scrub. Axis 27 10 •

+ + 0 • • • •• • • 0 50 • • 3 • 0 0 0 eo •• 0.• 0 • 0 ••

.,. .,.

Axis 3 100

0 .,..,. • 0 0 o 0 .,. • • 0

• "'. 0 50 COO 0

0 0 0 0

.,.• .,. Axis 2 0 0 100 28

grassland sites (e.g. Plate 2.2) I A. fissistipula in streamside sites

(e.g. Plate 2.3), A. glabra on screes (Plate 2.4) and A. inermis in stream-

side sites (Plate 2.5). Streamside habitats included some drier sites

where there were gravel soils which had very little slope. It is in these

sites, not necessarily adjacent to the streams, where A. inermis was most

abundant. A. profundeinaisa has no apparent site type preference although

its presence in a grassland habitat is shown in Plate 2.6.

TABLE 2.2 THE PRESENCE OF ACAENA SPECIES IN SITE TYPES. (N.B. The totals for each habitat type are not necessarily the sums of the frequencies of each Acaena species. This is because some quadrats had more than one Acaena species, whereas others had none).

Grassland! Streamside Scree Total X2 d. Scrub

Total 52 40 60 152 quadrats

Acaena caesiiglauca 7 2 16 25 7.28*

Acaena fissistipula 32 5 11 48 22.73***

Acaena - glabra 20 1 21 51. 45*** Acaena inermis 5 - 1 6 6.62* Acaena profundeinaisa 6 3 6 15 0.38 ns

cL 2 (0.05) .X z. 5.99 X22 (0.001) 13.82

Observations from the Amuri Basin

The habitats of the five Acaena species at Amuri are similar to those at Porters Pass. Each species appears to have distinct site type preferences.

A. glabra is only found on scree slopes and exposed gravely sites where there 29

Plate 2.2 A. caesiiglauca in a grassland habitat.

Plate 2.3 A. fissistipula in a streamside habitat. 30

Plate 2.4 A. glabra in a scree habitat.

Plate 2.5 A. inermis on coarse gravel. 31

Plate 2.6 A. profundeincisa in a grassland habitat. 32

would be good drainage. A. fissistipuZa and A. profundeincisa are found

in drainage channels and streamside sites but A. profun~eincisa also grows

on bare gravel soils. A. caesiigZauca is not very abundant in the basin

itself, probably because of the dominance of ChionochZoa austraZis on one side

of the basin, but occurs at lower altitudes in intertussock grassland sites.

Both the ~pined and unspined forms of A. inermis grow in more open areas,

especially on gravel at the road side' where there are few other species.

Plant material from these populations, as well as those from Porters

Pass, were collected and grown in a greenhouse at Christchurch, so that they

could be used for experimental purposes.

2.3 RELATIONSHIPS WITH ORGANISMS

2.3!1 Mycorrhiza

Roots of the five Acaena species from Porters Pass were examined

using the procedure of Phillips and Hayman (1970). This involved heating

0 short segments (approximately 1 cm long) at 90 C in 10% KOH for at least

2h., washing with fresh KOH, bleaching with H20 ~ and staining with trypan

blue in lactophenol. Endotrophic mycorrhizal fungi, of the vesicular-

arbuscular type, were detected in all five species (Plate 2.2).

2.3.2 Herbivores

Wild rabbits have been reported to eat Acaena ascendens on an island

in the Southern Indian Ocean (Derenne and Mougin 1976). Therefore it is likely that hares (Lepus europaeus)~ which are abundant at ,Porters Pass,

~at the Acaena species there. The mealy bug (Pseudococcus araecae), omnivorous species of toticid and nocticid caterpillars and a species of white fly, are also known to feed on Acaena (Miller 1970). A species of sawfly (AnthoZcus variervis) was introduced ,in the 1920's for the biological control of Acaena species as the seeds can depreciate wool quality consider- 33

Plate 2.7 Whole mounts of roots showing endomycorrhiza. (a) A. aaesiiglauda : (x200) (b) A. fissistipuZa (x200) (c) A. gZaq:ru (x200) (d) A. inermis (x200) (e) A. profundeinaisa (x250). ar = arbuscles, h = hypha, v = vesicles. Q

.~ ,...... ,~. " t~. ~ I" ' ....{ I '" • . -' ~d 35

ably (Hol 1964) . Gras hoppers nit?:dus) (identified by

G. Sandlant) were also observed to graze on leaves at Porters Pass.

The long-tailed cuckoo is known to eat Aaaena seed

(Gill 1980).

2.3.3

of rust fungi are known to occur on Acaena I namely

Phl'agmidium subsim'i Ie on A. Zauaa and PhY'agmidiwn aaaenae on A. micmphyUa (Dingley 1969). Phl'agmidiwn acaenae was also observed on

A. g~ahl'a and A. pI'ofundeincisa durincj this study I as well as Phragmidiwn novae-zeaZandiae on A. caesiigZauca. 36

CHAPTER 3

SEED ECOLOGY OF ACAE'NA

3.1 INTRODUCTION

One of the major factors influencing establishment of species in

any locality is their potential to propagate by seed. In emphasis the

importance of eeds to flowering , Heydecker (1973) states that:

"a seed is an end and a beginningi it is the bearer of the essentials of

inheritance; it symbolises mult ication and d I continuation and

innovation, survival, renewal and birth", Even if qnantities of

seed are produced still a mechanism for dispersal.

by seed is also restricted by viabil , dormancy mechanisms and removal or

ury to seeds by various animals and microorganisms. This chapter compares

the relative ions for and the factors controlling at ion in the five species of Acaer~.

3.2 MORPHOLOGICAL ADAPTATIONS FOR DISPERSAL

Seeds of the five Acaena species have been described in section 2.1.

However, the relevant tions for d sal will be discussed here.

Acaerla caesiiglauca~ A. fiss-istipula and A. profundeincisa all possess seeds with 4 barbed spines which are adaptations for zoor.horous

sal (Stebbins 1971). The absence of manunals in New Zealand, until recent times, would have restricted such dispersal to bird vectors. Nowa- days attachment to 's wool and fur of mammals such as rabbits and hares, would aid dispersal. Wind and streams may also be important agents.

Al though A. inennis develops , they are unarmed, so that

sal by attachment to animals would be less effective. Furthermore, when the seeds of A. caesiiglauca~ A. la and A. profwuie'inoisa are mature, the heads become very loose and shatter easily. In contrast,

the heads of A,'inennis rema,in intact and persist on the parent plant throughout the winter following production. The seeds of A. appear

to be less specialized for di than the other species.

The seeds of A. g are compressed, so that wings develop from each angle of the achene. The two lateral wings are more conspicuous, giving a flattened appearance to the seeds. The spines have also become reduced. Such modifications promote dispersal by wind which would be advantageous in a scree environment, where high wind velocities are frequent

(Fisher 1952).

3.3 FAC'l'ORS CONTROLLING GERMINll.TION

3.3.1 tion

Germination of seeds is often controlled so that its timing coincides with conditions favourable for seedl establishment. Many factors regulate the germination process, but among the most important are temperature, light and water availabi as well as innate dormancy mechanisms.

Each factor will be examined separately, for the sake of simplic and

clarity I but several independent or interdependen't mechanisms may be simultaneously in a s seed (Vegis 1963, Lang 1965, Stokes 1965) and their intensity and duration can vary within a popUlation (Maguire 1976).

Since seeds usually possess specific requirements for germination, the absence of the appropriate conditions or the presence of dormancy mechanisms will cause in the onset of germination, Delayed or sporadic germination would be advantageous for propagation in a changin91 unpredictable environment. Germination would be spread over an extended time period thus increasing the probability of seedling survival. Simultaneous germination of many seeds may result in mortality if adverse conditions arose. 38

Dormancy mechanisms are numerous and can be classified into three

categories: induced, enforced od innate. Induced and enforced dormancy

on the interaction of the seed with its environment. Induced

dormancy may develop nondormant seeds in response to certain environmental

conditions and continue even after those conditions are removed. Enforced

dormancy results from unfavourable environmeLtal conditions and germination

can proceed only when become favourable. Innate dormancy mechanisms

are genetically controlled and may be due to anyone or more of the following

(Amen 1966) :

(a) rUdimentary

(b) iologically immature embryos,

(el) seed coats to water and/or gases or

(e) mechanically resistant seed coats to embryo

In (a) anel (b), s ln the embryo itself are necessary while post

maturation processes take In contrast, the dormancy mechanisms in

through processes of 'weathering'. Such mechanisms are of survival value particularly where the conditions conducive to weathering occur in the

season which preceeds that most favourable for seedling establishment

(Koller 1964).

The addition of growth regulat hormones such as gibberellic acid

(GA 3 ) and kinetin are well known to overcome physiological embryo dormancy

in many species (Koller et aL. 1962 f Lang 1965, 1980) and are thought to be closely linked with light and temperature responses (Stokes 1965/

Wareing et .1973),

Nitrate solutions are recognised as major dormancy-breaking agents

(Steinbauer and GrigsLy 1957/ Toole et aL. 1956), but little is known about the actual mechanism involved (Thomas 1977). 39

Seed coat dormancy may be due to the restriction of gaseous exchange,

water or mechanical resistance to embryo expansion (t.jaguire 1980).

However, it is difficult to distinguish between these three mechanisms

since are closely associated. Well known methods of overcoming seed

coat include mechanical and chemical scarification, heating,

digestion and solvent treatment (Khan 1977).

Altbough such treatments may reduce seed coat impermeabil , they may also

induce other changes such as the sensitivity of seeds to light and

, possibly destroy or aid removal of inhibitors and damage living tissues.

An investigation of dormancy characteristics therefore involves the simulation of mechanisms as would occur in nature. Such a study is not only of value in elucidating the presence of particular dormancy factors, but also allows germination to be increased so that numerous seedlings of even age can be produced for other experiments.

3.2.2 Materials and methods

Large seed collections of the five Acaena species were made from

Porters Pass on 16. 3.80 and stored in paper at room temperature until required. In all s, except those us the thermogradient bar, two replicates of 50 seeds each were on Nhatman nwnber 2 filter paper with 2-3 rum of white sand underneath, in 9 cm diameter petri dishes.

These germination were maintained in a moist condition by the addition of dlstilled water when necessary. Germinated seeds (radicle emergence) were counted and removed every second day until the cumulative germination reached a plateau. For most experiments, a of 50 days was sufficient.

Spined seeds of Acaena iner'mis were used in all s. 40

Immediately after collection, viabil tests were performed at

0 20 C in a room under a 16 h.day: 8 h.n photoperiod with a light

intensity of 190 microeinsteins m- 2 sec~l . This was repeated 6 months

later with seed stored at room temperature.

responses were determined using fresh seed germinated at

0 and 32 C using a thermogradient bar in the growth room

conditions described above. The width of the bar restricted

space so that 2 icates of 25 seeds each in 4.5 em diameter petri a dishes could be used. The response to alternating (20/15 C)

was determined us a growth cabinet under 16 h. : 8 h.night photoperiod,

with a light intensity of 180 microeinsteins m 2 sec..1 At the same time

appropriate controls were in aluminium foil to determine if light

has any effect on The effect of cold storage (stratification)

on germination was evaluated using seeds stored at - C for 1 ar,d 2 months

in sealed petri dishes before being transferred to room e (approx-

0 imately 20 C) for ion. Controls were stored at roomtel11perature

and placed on after 1 and 2 months to the

stratification treatments.

The influence of moisture availability on germination was tested

using osmotic solutions of mannitol. Although mannitol is known to be

taken up by seeds (Lawlor 1970), it was chosen as the osmoticum because it

has advantages over other used solutes. Sucrose is very e, while polyethylene glycol may have serious toxic effects (La,,,lor 1970).

Germination of 6 month old stored seed was examined using ation pads soaked in mannitol solutions to osmotic potentials of

0, -2, -7 and -11.5 bars (Lawlor 1970).

The presence of physiological was examined by treatments

with GA3 and kinetin. Seeds were soaked in 10 or 10- 3M GA3 for 24 h'l or 10-4 M or 10-3 M kinetin (6 furfurylaminopurine) followed by a rinse

with distilled water. Seeds soaked in distilled water served as controls.

Seeds were left to germinate at room temperature under natural daylength

and light intensities for March/April I 1980.

The effect of KN03 was investigated by mo germination

,-,i th 3 m2 of 2% (w/v) KNO) at the beginning of the tal period.

This experiment was conducted under identical conditions and at the same

time as those examining the effects of GA3 and kinetin, and utilised the

same controls.

In an attempt to reduce the in onset of ion by removing

any possible dormancy effects associated with seed coats, seeds were soaked

in 50% (v/v) ethanol or 10% (v/v) Hcl for 15 minutes, followed by wash

with distilled water. were then allowed to germinate at room

ature under natural and light intensities.

A. 'ine:pm-is seeds did not germinate in any of the above experiments.

Therefore additional experiments were carried out using A. inel~is only.

Seeds which had been stored at room temperature for 5 months were put out a on germination pads which were maintained at 25 C by a water bath (a Copen- hagen type germinator) and left for 22 weeks in daylight. Trials were also conducted on seeds left in the dark at 00, 50, 100 and C.

During ion trials, a brown exudate was observed to leach from

A. inermis seeds. To test whether this substance may have an inhibitory effect on ion, 1000 seeds were soaked in 40 m2 of distilled water for 24 h._ The effect of the resulting exudate on the ion of other spec ies ,'las examined by add 3 m2 to germination pads and with distilled water treatments. The species tested were Acaena lauca ..

A. fiss-ist-ipu A. glabra~tomato (Lycopersicon esculentwn 'Amor'), radish

(Rlu:zphanus sativus ! S topl igh t ') and carrot carota 'Manchester Table'}. 42

In addition I seeds of A. inermis \·;e re leached by being suspended in nylon bags under a dripping tap for 12 days and their germination compared with that of unleached seeds.

The presence of seed coat effects was examined by lightly sanding with emery paper or nicking A. inennis seeds in random positions and com paring their germination with that of untreated seeds.

3.3.3 Results and analysis

Seed viability

There \Vas no change in seed viability after 6 months or dry storage

('Table 3.1). However seeds stored for 10 months at room temperature failed to germinate after 50 days although a fe\V seeds germinated sporadically subsequent to this. A. 'z:nennis did not germinate within the 50 day period and the germination of A. profil1~eincisa was less than the other three species

'TABLE 3.1 EFFECT OF STORAGE ON SEED VIABILITY. Mean % germination

after 50 days ± standard deviation with comparisons by t' test.

Fresh Seed Stored 6 Months tis C(

A. caesiiglauca 56 ± 12 33 ± 6 2.42 ns

A. fissistipula 68 ± 4 70 ± 6 0.39 ns

A. glabra 66 ± 8 62 ± 2 0.69 ns

A. inermis 0 0

A. profundeincisa 24 ± 10 6 ± 2 2.S0 ns

a. t's O.OS 12.71 43

The response to temperature 'das similar in all species (Table 3.2,

3.1) except A. s which did not germinate within 40

Germination of the other ies occurs in the range of 14-2 C with the

exception of A. which did not germinate at 2 Maximum

germination occurred at for A. ppoJunde~ncisa and at 17-2 for

and .4. glabra. In A. gZabra

had the highest total tion and the fastest germination rate, whereas

A. p!lofundeincisa had the lowest total germination (apart from A. i.neY'mis) t

(Fig. 3.1).

There was no s difference in germination response to

0 alternating tures ) compared ,'lith 17 or 2 constant

temperature (Table 3.2) . This is in contrast to the results found for

I1caena rnagel and A. where al ternating to

increase of these species (Walton 1911).

to cold

Cold storage has no effect on germination (Table 3.3). Walton

(1917) also concluded that cold pre-treatment was not necessary for the

germination of seeds of A. tenera and 11. magellan'ica. CertainlYt seeds

of the Acaena species from Porters Pass would not experience prolonged

, 0 winter as low as -25 C t but it is interesting that germination

was not by storage at such a lo~

Germination was significantly greater and occurred faster in 1

than in the dark for A. caes'iiglauca, A. la) A. glabra and

A. pr'ofundeinc'isa (Fig. 3.2). There was also no germination of A.

in the dark after 22 weeks. A light ement in these species from other populations is also implicated in trials by M. J. A. Simpson 44 100 A caesiiglauca

21" 50 11° r I 5(% 1%

100

LSO 21- 50 III I I S 50/0 1 .--i-.. tJ .c:: 0 t-.~ {J5 100 (/!.

50 LSIJ. l1t I I 5c;;o 1% 0

A. profundeincisa

LSD

1 I 21'" ~~~~:::::::::::::::::::: 14- 10 20 30 40 Days

3.1 Effect of on germination. 45 1

50 L.SD.

;c r 5%

100 A. fissi$/fputa

50 L.S.D.

100 ci?

a LS.D. ~, ~, .... ---~

J: I 5% 1%

0 ~-,

100

LSD. 50 Light r I 5% 1% 0 10 20 30 Days

f' 3.2 Effect of light on germination. L.L'.L: LA_-,- Vr: '-VL~'::> J.nL~.L nL~LJ TbLVl.l:' bt

0 j80 17° 2 25° 2 17v's 20 21v's 20 /15 r A. o 8± 0 46± 18 52± 12 8± 2 o 7 1.10 ns 0.92 ns

A. o 12± 4 46± 26 56± 12 4± 2 o 61± 1 0.82 ns 0.59 ns

A. g o 44± 20 64± 8 58± 10 12± 6 o 56± 2 1. 37 ns 0.28 ns A. o o o o o o

A. pY'ofundeinoisa o 8± 2 24= 6 12± 4 o o 43± 3 4.01 ns 8.77 ns

TABLE 3.3 EFFECT OF COLD STORAGE FOR 1 AND 2 MONTHS ON Values are mean % deviation 1 Month 2 Months Cl Control t. 's

A. oaesiig 52± 10 18± 12 3.08 ns 22± 4 341: 8 1. 90 ns

A. f~ssistipula 34± 4 48± 10 1.84 ns 26± 20 14± 2 0.84 ns

A. gLabra 30± 16 22± 20 0.44 ns 60l 10 68± 8 0.88 ns

A. inermis 0 0 0 0

A. 7± 4 2± 2 1. 58 ns 4± 4 24± 10 2.63 ns

Ci t's 0.05 12.71 (j."" 47

Division, D.S.l.R.) I al A. ,'las not tested.

The effect 0 water avai

All five Acaena failed to germinate in water tensions above

-2 bars (Table 3.4). In comparison with other tussock grassland species which are capable 0 germinating at -11.0 bars (Makepeace 1980)/ these

Acaena species have a high water requirement_ for germination.

TABLE 3.4 THE INFLUENCE OF WATER AVAIIABlLrrY ON GERMINATION.

0 bars 2 bars -7 bars 11.5

caesi'ig ZaucCl 31± 9 0 0 0

A. Za 83:1: 6 12± 6 0 0

A. 63± 10 18± 4 0 0

A. inermis 0 0 0 0

A. pro fundeinc'isa 61 4 0 0 0

Re and Kinetin

kinetin are shown in 3.3 and 3.4 respectively. The germination of

A. caesiigZauca increased in response to 10-3N but increases were not observed with kinetin. Both the rate and final germination of A. fiss tipula were increased in all hormone treatments, suggesting that some seeds may be phys ly dOl~lllant. The of A. glabrCl only with,

A. pT'ofundeincisa did not respond to any of the hormone treat- lIlents and these treatments did not induce the germination of A.

Re . . Table 3.5 shO\<1s that the ion of A. l.nerm·~8 ,vas increased

\vhen seeds were treated with 2% (w/v) KN03' 100 48 A. caesiiq!o.ucG

50 LSD.

I I 5% 10/0 0 100 A. fissis Noula i

L5.a 50 I I

1% c: C) -\...... -- CJ 0 . --.c::: E:; ~ 100 ~ ~

100

0 10 20 30 40 50 Days -4 Figure 3.3 Effect of 10 M and 10 Hie acid (GA ) 3 on ion. -4 3 10 M GA3 f !'--A 10 M GA3 ! ~ control. 49 100 A caesiig/a uC a

LSD. 50

I: I 570 JOlo 0 100 A fissis tip u{ a

L.S.D, 50 I I 50/0 10/0 ',,::a a .S; 0 E di LS 100 A glabra '(f!. L,SJJ. 50 I

50/0

100 A ,Qrofund eincisa

L.s.a 50 I I 5% 10/0 0 10 20 30 40 50 Days

Figure 3.4 Effect of 10-4M and 10-3M kinetin on germination. -4 1 -3 k' . 0----0 10 M kinetin I !!!---m 0 M lnetln, '1!>--4 control. 50

TABLE 3.5 EFFECT OF 2 ON GERMINATION.

Values an~ mean rmination after standard deviation

--_..... ex Control 2% KN03 t l

A. 33 5 29± ] 0.9

fissistipula J01: 10 5]± 3 3.1

glabra 27 0 40± i! 4.

; inermis 0 47± 1 66.4

. pl'ofundeincisa 3± a 6± 1 4.

a s Cl.OS 12.71 t' s 0.01 63.66

The effect of ethanol and acid

Soaking seeds in ethanol increased germination in A. and A. glabra whereas treatment with HCl increased germination in A. caes~~-

and A. glabloa (Fig. 3.5). This suggests that there may be some seed coat dormancy in these species. The decreased ion ::esponses shown in Some situations are pass due to inhibition 0 development by these chemicals.

Additional to A. inermis . . Several seeds of A. '/'nenrns in the light at 2 after a period of 10 weeks; a considerably than for the other species.

Then:: was no germination of A. inermis seeds .in the dark at 0, 5, 10 and after 22 weeks.

The brown leachate obtained from A. seeds had no effect on the germination of A. caes'i'igZ.auca~ A. laJ A. glabra tomato, radish or carrot (Table 3.6). 100 5

L.SD. 50 I I 5% '/010

100 A, fissistipula

LSD. 50

l' I 50/0 0

100 A,q(abra

L.SD 50

r SOlo

100 A. profundi? {~isa

LSD. 50

10 20 30 50 Days

Figure 3.5 Effect of 50% ethanol and 10% HCl on germination

0-0 50% ethanol, ~ HCl, e---

TABLE 3.6 THE GERlHNATION RESPONSE AND A. AFTER 50

AFTER 6 DAYS, i'iHEN TREATED ~nTH A. INE'RMI8 SEED LEACH..:il;,TE. Values are mean % ± standard lon.

ct Leachate Distilled Water tis

A. cae siigZauca 14 ± 4 f, 0 2.12 ns

A. fis siat'ipuZa 35 ± 1 39 ± 1 4.00 ns

A. 64 ± 6 67 ± 5 0.54 ns

Tomato 77 ± 1 79 1 2.00 ns

Carrot 83 ± 3 81 ± 5 0.49 ns

Radisl1 100 ± 0 99 ± 1 1.41 ns ... - .- at' 0.05 12.71 5

There was no germination of A. after 60 days when seeds had been leached, sanded or nicked. Therefore, there is no evidence that seed coat effects are involved in de ing germination in A.

3.3.4 Discuss

Several factors appear to control the seed germination of the Acaena species from Porters Pass. The restriction of germination in all species to warmer temperatures (Table 3.2) would ensure that germination could only o occur between October and Harch when soil temperatures are above 8 C

(Holloy 1963). Germination in autumn may not ,result in successful establishment of seedlings since seedling survival would be hampered by too little root and leaf growth to withstand the cold winter. Because of this, many

~oeedl in tussock grasslands are known to die in response to drought and frost heaving (Simpson 1957). Since there was no germination at SoC, the response to temperature alone would prevent wasteful germination during winter. The lower temperature optimum for germination of A. pY'ofunde-inc-isa seed is consistent with its ability to inhabit higher altitudinal sites compared with the other (section 2.2.1). 53

stimulated rmir;at,lon in all species. This would restrict

germination to the surfac~ of soil or to bare tes where :.:-:ere is

little shade from other ~l ts. Such a requirement is common in ::::.ost bare

ground colonisers ime nd Jarvis 1975) and weedy S{J:, and

Wareing 1969) and would be an advantage in sites which are dis-

turbed or when the 1 of the seedling or mature plant for competition

with its ne lS 10',.,. Periodic erosion processes occurring in the

high country would therefore favour seed germination.

Germination of A. tauca, . fiBSis A. glabra dnd

A. profuruieinc'iBo is res icted to extremely moist conditions (Table 3.4).

Not only would this restrict to Doist sites, but also to certain

times of the year when soil 'dater is readily available. Accordi:':; to

prec tation and il water evaporation data for Foggy Peak (.'10110y

1963), soil water leve suitable for germination of these eS' Jxe most

likely during Harch to November. However as already shown, the te:::"perature

responses would prevent nation during the winter months. Therefore

the interaction of temperature and water may limit germination

to October and November.

Promotion of germination in A. j'issistiputo by both GA3 and kinetin

strongly that some seeds have physiological dormancy mechanisms

and require 'after ripening' before germination is initiated. Germination

of A. aaesiigtauea and A. glabra may also be controlled by physiological dormancy since there was also of germination by GA3 in these

species.

The lack of consistent effects of GA 3' kinetin and }

species may be attributable to the lack of absorption of these sub5tances

into seeds, especially when some seed coat effects are apparent. In this respect, of A. fissis and A. g was by ethanol, 54

and in A. oaesiiglauoa and A. g by Hel treatment. Walton (1977) found

that treatment of A. tener'Q seeds with 50% ethanol or

50% 0 did not reduce the de in onset of germination nor increase 4 their total germination. Nevertheless, seed coat dormancy is very common

in plants from high altitudes and has been related to the frequency of soil

dis'turbance in these habitats (Amen 1966). Abrasive action produced by

solifluction (freeze-thaw) and wind would aid the breakdown of seed coats

in nature.

Germination of A. inennis is delayed compared with the other species.

Since there appears to be no cold requirement, no after-ripening nor seed

coat factors involved in the seed dormancy of this species, the cause 0 delay in germination can 0 be It is interesting that the

germination of A. inermis was hastened by the addition of However

little is known about the mechanism involved (Thomas 19~'7).

Delayed and extremely sporadic germination of A. inermis seeds may decrease

the probability of chance annihilation of a proportion of 'potential

Therefore the chance of survival of the species is possibly increased by staggered germination over several years. Germination of

A. inermis is known to continue until at least 41 weeks after the beginning of a trial (M. J. A. Simpson pers. comm.). Such delayed germination is not uncommon in seeds of plants from high altitudes. Mark (1965) found that although only 31.5% of ChionoohZoa rigida seeds germinated after 50 germination continued until ly four years later when 94% of the seed had germinated. Cook (1980) concluded that on important demographic property of seeds is the great variation in the capac to remain dormant and viable in the soil. Amen (1966) goes so far as to say that species which possess seed dormancy mechanisms are like to be more successful than species without such adaptations. However it should be remembered that

germination increases the chances of viable seed loss to soil animals 5

and microorganisms. This may be overcome to some extent in 11. inePmis by

the retention of seeds on the parent over the winter.

Although it is well known that there are physiological adaptations which would control germination so that it occurs in sites and seasons

favourable for seedling establishment, the role of germination in maintaining populations is unknown. Seedling establisr.ment in slow perennials may only need to occur sporadically for a population to be maintained

(Billings and Mooney 1968). Vegetative tion by stolon production probably plays a or role in maintaining Acaena populations. However this is unlikely to be important in A. g which does not have

and root tendencies of the other 4 species. Germination in this species is con istently good and more than the others, indicating that it is more reliant on propagation by seed. 56

CHAPTER 4

COMPARl\TIVE RESPONSES 110 WATER S'l'RESS

4.1 INTRODUCll ION

Ecological differences in the distribution of species are often

related to the water availability of their habitats, since water is essential

for establishment and survival. Water s is almost

present in higher due to an excess of transpiration over

absorption (Kramer 1969). This ultimately modifies plant f as the

internal water deficits affect many physiological processes

either directly or indirectly.

Huch of the ecophys work could not establis~ general

relationships between morphological structure, transpiration and habitat

with respect to soil moisture. For example, Schra":z (1932)

found that some ericaceous plants showed xeromorphic characteristics and

others mesomorphic ones, he could not relate their structure and

ation rates to their habitat It seems likely I that trans-

piration rates would a better indication of the plant's response to

the aerial environment. Adaptations for water absorption will also be

in determining the range of habitats in which can live,

since internal water contents will depend on the balance between absorption

and transpiration.

According t.o Levitt (1972) f drought resistance can be divided into drought avoidance and drought tolerance. The former is mainly achieved

through morphological adaptations, whereas the latter concerns the plant's ability to remain physiologically active in dry conditions. Host. terrest- 57

rial plants probably develop adaptations in each category to varying degrees.

The extent of adaptation will determine the range of conditions in which

any species can survive. Plants for resis water stress have

been further subdivided into 'water , and 'watel: savers' (Maximov

1931) . 'Water spenders' are able to survive in high evaporating conditions

if they have efficient root absorbing systems and an adequate water supply

to maintain high transpiration rates. 'Water savers' also tend to have

efficient '.'later absorbing , but conserve water by reducing transpir

at ion rates (Maximov 1931). Therefore the relative control over transpir-

ation will dictate the strategy of each plant.

The control of water loss is ly achieved by stomatal closure,

but xeromorphic characteristics may also assist in Hater conservation.

Extensive development of cuticular ',.1:lxes may reduce cuticular water loss,

either di (Martin and 1970) or indirectly through the reflect

ion of 1 , so that leaf are not unduly increased (Pearman

1966) . The presence of epicuticular hairs may also be involved in water

conservation by maintaining a more equable water vapour over leaf

surfaces. They physically shield stomata from high conditions

or reflect light, thereby preventing excessive increases in leaf temperature

(Billings and Morris 19.51, Parker 1968). The number and distribution of

stomata may also be informative about the water relations of plants. In

a survey of stomatal frequencies of woodland plants, Salisbury (1928)

concluded that the number of stomata per unit area may vary depending on

the amount of growth, particularly of the epidermal cells. The absolute

number of stowata may be h if there are numerous small epidermal cells.

Conversely, a low stornatal frequency may be due to growth of the

epidermal cells which would tend to inc.rease the distance between stomata.

The concept of 'stomatal index' takes these factors into account by relating 58

the number of stomata to the nwnber of epidermal cells per unit area

(Sal 1928) 1 and tends to remain fairly constant for anyone plant

(Meidner and Mansfield 1968).

The degree of stomatal control over Ivater loss may indicate the

abil of a species to withstand water stress (Bannister 1976). This

can be observed by following the loss of water from excised, turgid leaves.

As water is lost from leaves, the subsequent internal phys ical condit-

ions result in stomatal closure, thereby a decline in the

ation rate. ~'lhen the majority of stomata are closed, water loss is prim-

arily confined to that which escapes through the cuticle. The response

of stomata to internal water deficits is therefore likely to be crucial in

determining photosynthetic activity, since gas exchange is vital for this

process. The use of excised plant to examine the control of water

loss has an advantage over other gravimetric methods by al -::he trans

regulating mechanisms to exert their full influence during the

experiment (Hygen 1951, 1953). Other techniques using continued water

absorption during the experiment, would tend to postpone or the

functioning of such regulating mechanisms.

Bannister (1964) modified 's approi:l.ch and expressed the water content decline of cut shoots as a percentage of the initial saturated water content. This allows the water content values to be independent of dry weight, which may vary considerably with age and kind of tissue.

Bannister (1964) has shown that although the rate of transpiration depends

"n the evapora conditions, stomatal closure occurs when a critical amount of water has been lost from the plant and that this is ndent of the external conditions. Therefore, by this critical level

(i.e. the relative water content at stomatal closure), differences between

, responses to water deficits can be examined. 59

The responses of different species to water loss have been related

to the moisture regime of their habitats. Plants from moister habitats

tend to have higher relative water contents at stomatal closure than those from drier habitats (Bannister 1964, ~1ooneyt al. 1965). This confirms earlier beliefs that ants from drier habitats longer and tolerate water los for the sake of maintaining open stomata and conse- quent photo activi ty (Maximov and Krasnoselsky-Maximov 1924).

Thus differences between the responses of species to water deficits may account for their apparent habitat preferences in nature.

Field evidence (section 2.2.3) that the distribution of

ACael'ICl species at Porters Pass and Amuri might be related to their watec relations. Therefore, this examines the relative responses of each species to water stress. The following features were investigated:

(1) a comparison of the growth of seedlings in different water tensions,

(2) the relative control over stomatal aperature when leaves are exposed

to water deficits and

(3) various morphological characteristics likely to be important in the

I water relations.

4.2 MATERIALS AND METHODS

4.2.1

Germinated seeds of the five Acaena species were pricked out into

5x5 em plastic pots containing 350 g of potting mix (Appendix II). There were three icates for each of three water regimes, which were maintained

Ly pots to predetermined weights, based on a water tension versus water content curve determined prior to the inning of the experiment

(Appendix II) The seedlings were grown in a Sherer CEL B growth cabinet

(light inten 180 microeinsteins ~2 secl at the soil surface; 16h day

0 at O± 2 Ci Bh night, 15± lOCi humidity always above 60%), for 5 weeks before 60

o being harvested, dried (95-100 C for at least 24h) and weighed to the nearest 0.00005 g.

4.2.2 Re se to \1ater loss fnJm excised s ~-~------.. ------The approach used was that of (1953) and Bannister (1964) where the water loss from excised leaves was :neasured over a period of several hours by successive weighing. Young shoots were collected from the field in 1980 and immediately placed in jars of water, where

remained for 24h to reach full turgidity. The leaves were exposed to light for at least 5h prior to the beginning of the experiment to ensure that the stomata were open. Transpiration decline was estimated for each species using 3 replicates of 10 leaves placed on a petri dish with abaxial surfaces uppermost. 1>1easurements on individual samples were staggered in order to obtain values for each species over the same time period. Samples were weighed a Mettler balance (to an accuracy of 0.00005 every 5 minutes for the first 20 minutes and every 10 minutes thereafter, for a total of 3 hours. The temperature (16.5 ± 1. SoC) and relative humidity

(70 ± 1%) did not vary markedly throughout the experiment. The relative humidity was measured using a whirl psychrometer. After the experiment, o samples were oven dried at 95-100 C for 24 hours and weighed.

4.2.3 Examination of characteristics

Macromorphological features have been described in section 2.1.

Only micromorphological features, as observed under the scanning electron microscope (S.E.M.) are presented here. Initial at us epider- nBl replica techniques to observe leaf surfaces were rejected due to the smallness and ha nature of leaflets. Examination of stomata using the light microscope was also abandoned. Although stomata could be observed after bleaching with acidified sodium hypochlorite or 'Carnoys' fluid (60%

ethanol, 30% chloroform and 10% acetic acid) I epidermal cell outlines were 61

obscure and the tissues tended to disintegrate. Staining bleached leaves

with methylene blue resulted in the colouration f all cell layers, making

the epidermis indistinguishable. 'The most Gatis results were

obtained us the S.E.M.

Leaflets were mounted on aluminium stubs with double sided tape,

air dried and subsequently coated with a of gold before examination

using a Cambridge Stereoscan 600 S.E.M., 'l'l1e number of . stomata and epider

mal cells were counted on both leaf surfaces over a constant area (at 500 x

magnification) using leaves from plants grown in greenhouse conditions.

For the purposes of comparison between abaxial and adaxial surfaces, opposite

leaflets from the same leaf were used. Four counts on each of 4 terminal

leaflets were made. ~'lax structures of both the abaxial and adaxial leaf

surfaces were also observed on field plants as well as greenhouse grown

plants. All S.E.M. work was performed at only 5-10 kV to avoid to

waxes which would be caused by higher vol Photographs of the wax

structures were taken using a JEOL JSM 35 S.E.M. which gave better resolution

at 10,000 x magnification.

4.3 RESULTS AND ANALYSIS

4.3.1 Growth re in different water

The major problem with this of experiment is that water will not

be evenly distributed throughout the pots due to evaporation and water

at rqot surfaces. Therefore the soil water tension at the root surface may

vary from the values given for each treatment. Furthermore, it was not

possible to take into account the increase in weight of each pot due to

growth. 'l'herefore the values given for each treatment are only

approximations of the water tensions experienced by the roots.

The mean dry we of the five Acaena species grown in three different soil water treatments are in Table 4. L These were 62

transformed to log (dry we mg) before sis. Only two seedlings e of Acaena lauca survived, one in each of the drier treatments (water

tension 2.2 bars and -12.6 bars). Therefore the dry weights for A. cae8~~- glauca were not included in the analysis of varia.nce. A. Zauca dlso did not (::lstablish well on mix in other growth experiments

(section S. 3 .1) .

'l'ABLE 4.1 TREATMEN'r MEANS AND FOR GROWTH OF ACAE'NA SPEC IES IN DIFFERENT SOIL WATER TENSIONS AFTER 5 WEEKS.

Water Tension (bars)

-0.15 ± 0.05 -2.20 ± 1.90 2.4

"f caes'/>igZauca 2.14 1.

{issistipu 3.67 ± 0.89 4.36 0.21

gZabl?a 3.81 ± 1.91 3.59 ± 0.36

Q+ n inermis 3.67 _ 0.06 3.92 ± 0.11

pY'O fundeincisa 4.54 ± 0.32 2.33 + 1.28

+ n=l

Q n=:2

---.-_. e of variation df 1>1ean Square

ies 3 0.3446 O.

Tension 1 0.7938 0.8

x ~"'ater

ion 3 2.4785 2.7

14 0.9081

a (3,14 ) 3.34, (1,14) 4.60 .05 FO.OS 63

There was no significant difference bebveen species ',."hen grown in

average water tensions of -0.15 bars od 2.20 bars. However no seedlings

of 11. fissistipu A. glabl'Cl" A. or .4. profundeincisa survived in

the driest treatment.

4.3.2 to water loss from exised leaves

'r'he weights of each leaf sample were used to calculate relative

water contents (R) at time t by,

R x 100% where W is the weight at time t W is the initial saturated we and t f s Wd is the dry \veight of 10 leaves. The values are plotted over 3 hours for each icate (Fig. 4. The rate of relative water content Loss was calculated by,

x 100 per minute

and against time . 4.1b). Two constant rate phases cor res pond to the 'stomatal' and 'cuticular' phases can be recognised. The intersection between these two s is taken as the point of stomatal closure, although in real , stomata close gradually and all stomata do not close t the same time (Meidner and Mansfield 1968) The water content at stomatal closure was determined finding the intersection between the regression lines of the rates of water loss during the 'stomatal' and

'cuticular' (Bannister 1971) and were subjected to an analysis of variance 4.2) .

On the basis of previous observations, it has been that plants from drier habitats would retain open stomata over a wider range of water contents and therefore exhibit lower water contents at stomatal closure than from moister sites (Bannister 1964, Mooney et al. 1965). t.... QJ -I--.- Cj )::

QJ :::". 1

70 I • 2 QJ 'I , I 1 ct:: I , 3 .,I '• 6

I , I • I I I I I I I I , I I I I I I I I t : I I I I I I I I I I I i! I I I I I I I I a I

0,1

20 40 60 80 100 120 140 160 180 Time(minufes)

4.1 Relative water contents (a) and rates of relative 'Nater loss (b) of the five AeaeiifJ species. 'rhe intersection 0 the two constant rate phases in (b) indicate the points of stomatal closure and the relative water contents at this time are found

by extrapolation back to (a) for each icate, fin3t

Iik-"-_-"~Jl. third icate. :Lca te f 0---0--0 second icate, 65

100

t I' I ,I (a) I II 90 III II 'II I ,i :Ii I" I q I I, 80 I 'I I 'I " :1./ I !: I I, ! II I"I 01 70 , .1 , II

I, !!Ii Ii I II J ":1 I II 60 I :: ! :1 I I

20 40 60 80 100 120 140 160 180 Time(minufes)

Figure 4.1 Continued. 66

100

~ 70

0·7 b

(}6

~ 005 :::J()4

~ 0,] Q. '$. 0-2

(J.l ~Cftj·~p~~Et~ 13 o+~----r--~--;-----L-+---,---y----.....::;o:.-.r'2""'--O 140 160 /80 Time (minuf )

Figure 4.1 Continued. 67

100 it in e rJl1/s a

0·7 b

(}6

...... OJ ::::J c: "-E; 0 '- 03 o 0 QJ A ... 2 Cl. 3 * 1\ " 1

1 iiI' 1 20 40 60 80 100 120 140 160 180 Time(minutes)

Figure 4.1 Continued. 68

100 A.profundeincisg

f I OJ I ::,. 70 , I I I I I : " I',I I,

1'1i " III 60 I I, 1'1 III ~·---r-·--'---~'--~ It! 'II II' ''I : 'I b I"" III I II 06 III III III ', "f ' I' 04 I",II ,II ,II i"-, ,Ii III A. ClJa.3 I', Q.. ,I J I' ;j!. I II 0 0 (}2 I II" • 2 (}1 J 0 1 , , .---. 0 i • , I 20 80 100 120 140 160 180 Time(minu tes)

4.1 Continued. 69

Table 4.2 shm.,rs that the five Aeaena species differed considerably in the

water content of leaves at stomatal closure. A. 'inel?mis and A. proj'unde'in

had the lowest values, whereas A. la and A. g lahra had the

highest, with A. being intermediate. On this basis, A. iner-mis

and A. would be expected to be more tolerant of dry habitats

than the other species.

'rABLE 4.2 RELATIVE l'INrER CONTENT AT STOMATAL CLOSURE AND ANOVA.

Mean % R ± standard

A. inel'mis 81.17 ± 0.76 a

A. profirndeincisa 82.33 ± 0.28 ab

A. lauea 83.67 2.08 b

A. labra 93.00 ± 0.00 c

A. la 93.83 + 0.58 c

ANOVA

Source of Variation df Mean

Species 4 ll. .06 ***

Error 10 3.

F 0.001(4,10) 11.30 70

':tABLE 4.3 RATE OF INCREASE IN IvATER USING REGRESS COEFFICIENTS FRON FIG. 4.1b) AND ANOVA STQt'.1ATAL CLOSURE

AFTER STO~1ATAL CLOSURE. Nean increase in water loss ± standard deviation.

) (b) c- l -1 2 g min- g min X 10

-~--~.

caesiigZauca 0.0043 ± 0.02 0.0323 ± 0.13

j'issistipuZa 0.0150 ± 0.06 0.0189 ± 0.06

gZabra 0.0115 ± 0.10 0.0128 ± 0.10 . . '~neyrrrns 0.0062 ± 0.01 0.0153 ± 0.10

ppo fwuiwincisa 0.0131 0.06 0.0127 ± 0.09

... --

ANOVA

(a) (b)

.--.. --~~ Mean I;1ean of Variation df Fa s

ies 4 0.0063 1. 75 ns 0.0200 2.15

10 0.0036 0.0098

_..----

a F (4 , 10) 3.48 0.05

There was no significant difference between species in terms of the mean rate of increase in water loss (us the regression coefficients for

each replicate) 1 prior to and after the point of stomatal closure (Table 4.3).

This emphasises that transpiration rates alone are not very informative as to the comparative responses of each species to water stress.

4.3.3 Characteristics

The number of stomata and epidermal cells per unit area were used to calculate the stomatal index:

number of stomata unit area stomatal index x 100 number of stomata number 0 + per unit area epidermal cells per unit area 71

Table 4.4 shows that there was a highly s ificant difference between the

stomatal indices of the five Aoaena species, but there was no s ificant

difference between the upper and 10l'ler surf , nor leaves of the same

species. fl. 9 tohl'a had the stomatal index whereas ;~ae8

and A. inermis had the lowest.

A comparison of the number of epiderIr,al cells per unit area for each

leaf (Table 4.5) shows that the total number of cells not varies between

species but also between leaves. In fact, there were third order inter-

actions between species, leaves and leaf surfaces. These results emphasise

the nee of using st.omatc.l indicies f since the total number of epidermal

cells is variable per unit area and is probably a reflection of differences

in growth.

Wax structures of all five Acaena species consist of rods, clusters

of and platelets on both upper and 10\vcr leaf surfaces (Plates 4.1

and 4.2 respectively). In , the development of rods and granular

structures on the abaxial surfaces are more dense than on the adaxial sur-

faces. In addition, ltiaX structures are much less d on the adaxial

surfaces of A. gtabra and A. than the other

It is interest that similar development was found in the wax

structures of leav€"cs grown in both greenhouse conditions for 18 months and

in the field. Therefore, wax structures on these specie appear to be determined genetically rather than in response to environmental conditions. 72

TABLE 4.4 STOt-1ATAL INDICIES AND ANOVA. [

A. ineT'miG 13 .88 ± 3.62 a

A. lauca 14.65 ± 4.01 a

A. Pl'oj'undeineisa 18.78 ± 4.13 b

A. j'issistipula 19.67 ± 4.47 b

A. (JZdbl'a 21.87 5.70 c

ANOVA

Source of Variation df Mean Squa.re F: ._ ..

Species 4 3.7064 18.75 ***

Surfaces 1 0.4230 2.14 os

Leaves 3 0.1100 0.56 os

s x Surfaces 4 0.4117 2.18 ns

ies x Leaves 12 0.2536 1. 28 ns

Surfaces x Leaves 3 0.1671 0.85 os

s x Surfaces

x Leaves 12 0.1805 0.91 115

Error 120 0.1977

(4,120) 2.45 F . (4;120) 4.95 .05 o Ool F (1,120) 3.92 (3,120) 2.68 0.05 .05 F (12,120) 1.83 0.05 TABLE 4.5 THE NUMBER OF EPIDERMAL CELLS PER UNIT AREA AND ANOVl\j ± standard ion.

A. Hpu 98.91 ± 16. 56 a

A. g~abr'a 102.03 ± 20.35 a

A. profundeincisa 142.84 ± 24.89 b

A. caeBiigZauca 172.69 ± 25.10 c

A. inermis 189.88 ± 38.60 d

ANOVA

Source of variation df r-lean Square s

Species 4 53490.7906 78.02 ***

Surfaces 1 2648.7563 3.86 ns

Leaves 3 7745.5229 11.30 ***

ies x Surfaces 4 4068.9594 5.93 *** Species x Leaves 12 8591.3198 12.53 *** Surfaces x Leaves 3 2534.7896 3.69 *

Species x Surfaces x Leaves 12 2666.4719 3.88 ***

Error 120 685.5938

F . (3, 120) 3.95 F . (3,120) 5.79 O Ol o aOl

FO.OOI (12,120) 3.02

also see values given for Table 4.4 Plate 4.1 Scanning electron micrographs of leaf (adaxial surface) wax structures, (IO,OOOx).

(a) A. caesiiglauca (b) A. fissistipula

Plate 4.2 Scanning electron micrographs of leaf (abaxial surface) wax structures, (104000x). (a) A. aaesiiglauaa (b) A. fissistipula (c) A. glabra (d) A. inermis (e) A. profundeinaisa.

Bar = 1 ~m.

4.4 DISCUSSION

Seedlings ';Jere used to compare the growth of each species in

different water tensions because are likely to be more sensitive to

water stress than established ts (Jarvis and Jarvis 1963). Their gross

s are unlikely to aid water conservation and te small changes

in the environment may cause death. Only one seedling A. cae8iigZmwa)

was able to survive in drier conditions (Table 4.1). Establishment of

seedl in the field would therefore be restricted to when the

soil moisture status is suitable. Potential evaporation values for the

soils from Peak (Molloy 1963) indicate that a 'water deflcit' occurs

during and February so that establishment would be unlikely

during these months. However, of mature plants would not be as

limited, since mature plants in all species, except A. were observed

to I woody root systems in the field (section 2.1). This

would allow them to tap water supplies from deeper soil and possibly

store ,vater I so that excessive water deficits could be avoided.

It has been emphasised that the rate of transpiration does not

necessarily indicate a plant's to xeric conditions (Maximov 1931) .

Instead the of water loss through stomatal closure and through other morphological s may be more This is probably true

for these Acaena species since neither the stomatal nor cuticular rates of water loss differed between species (Table 4.3). The observed variation

in the degree of development of epicuticular waxes does not appear to affect

the rates of cuticular water loss. Nevertheless, the extensive development of wax structures is to reduce cuticular water loss and would be important in re light, so that damaging effects of high light intensities (a feature of t~eir habitats) and excess high leaf temperatures, can be avoided. 79

Leaves of A. 'inenllis appear to be more tolerant of water loss than

the other species. Although Salisbury (1928) and Parker (1968) state

that plants in xeric environments tend to develop a large nwnber of stomata,

presumably to provide a cooling system, a low number of stomata may also be

advantageous if water is to be conserved i.e. water loss reduced.

A. inermif} was not only more physiologically tolerant of water loss, as

shown by its ability to tolerate high water deficits whilst maintaining

open stomata (Table 4.2), but also had a low stomatal index (Table 4.4).

This implies that transpiration per unit cell is low and that A. inenl71:s

can be classified as a 'water saver 1 (sensu Maxiclov 1931) . In addition,

the epidermal cells of A. inermis are smaller, since leaves had a signifi-

cantly higher number of epidermal cells per unit area (Table 4.5). Small

cells are considered to have superior resistance to mechanical damage from

desiccation (Levitt 1972, p179).

The adaptations of A. inennis to tolerate water loss are consistent

with its presence in drier, open sites in the field (section 2.2.4).

However, in order to make comparisons of the degree of control of water

loss, it was necessary to use individual leaves, isolated from the intact

plant. Leaves rarely occur singly in nature so that neither their behav-

iour nor adaptive qualities can be accurately understood in isolation from other leaves. Gross morphological featUres and habit characteristics are

also likely to be important in nature. The low stature of A. inenllis and

the formation of mats would minimize the leaf area exposed to wind (Bliss

1972) (see Plate 2.5).

Assuming that the water content of leaves at stomatal closure gives a good indication of a species' ability to tolerate water loss, the next

Il10st tolerant species are A. profuncle1:nc1:sa and A. caesiiglauca. These species mainly inhabit grassland sites where water would not be as abundant o

as in streamside sites. Although A. aaesiiglauaa is not found in drier

more open sites, A. is less restricted to closed vegetation.

The soil surface conditions in grassland sites would be modified by shade

and litter production from taller statured plants (Scott 1962) thereby

creating suitable habitats for seedling establishment. The greater abund-

ance of eipcuticular hairs on A. and A. pi·ofuncleineisa may also

be advantageous in res desiccation.

A. fissistipula and A. g are comparatively less tolerant of

water stress than the other species. This may explain their preferences

for moister sites in nature (section 2.2.4). A. tipula vlaS mainly

found in streamside sites at both Porters Fa sand Amuri, whereas A. glabra

had a distinct preference for screes. Al screes are ect to high

evaporating conditions as a consequence of , high light

intensities and high wind velocities, Fisher (1952) has demonstra-:::.ed that

water is available in substantial amounts in the , non-mobile laye:cs

of screes. The coarse angular rock ,"hieh make up the surface

s also protect the underlying soil from (Weaver et al. 1927)

The development of long, woody root systems in II. g would enable it to make use of these water supplies.

A. glabra had the highest stomatal index (Table 4.4) which is strong

evidence that transpiration is greater in this species. High

rates would provide an effective leaf cool which would be necessary in high evaporating atmospheres. 'l'herefore A. glabl'a is tl 'water (Maximov 1931). The smaller leaflet size of A.

(section 2.1) I compared with the other species, may also be in reducing frictional resistance to the flow of water. This follows from the shorter distance of the mesophyll cells from the veins. As a result of the capac for substantial water absorption, the leaves would not be 81 subject to extreme desiccation so that stomata could remain open de losses due to transpiration, thus enabl continued C02 assimilation.

The more erect habit of A. g compared with the other species

(see . 2.3} and coriaceous nature of the leaves would be advantageous in a scree habitat where there is a danger of low statured plants being damaged by moving debris. HO'flever, an upr habit would result in greater exposure to wind and hence further increase transpiration rates.

Although creating high water losses, as previously mentioned, high transpiration would be of advantage in reducing leaf temperatures. The small leaf angle in A. glabra (Fig. 2.3) means that the leaves are more 1 to incident light which may ensure that they are less readily heated

(Shields 1950).

As leaves of A. glabra out, the adaxial surfaces come

This tendency was also observed in the other species but was not as pronounced. Such a response to desiccation would have obvious advantages in reducing the surface area exposed to wind and high light intensities. 82

CHAPTER 5

GROw~H IN RESPONSE TO SOIL QUALITY AND NUTRIENT SUPPLY AND GROWTH RATE ANALYSIS

5.1 INTRODUCTION

Comparative growth analyses are often informative about the require-

ments and environmental of species, since optimal growth occurs

in the most favourable conditions. Edaphic factors of the environment are

vitally important because of the intimate contact between individual plants

and the soil. Every facet of soil chemistry and physics affects the indiv-

idual to some extent by determining the availabiLity of essential

requirements, particularly water and mineral elements. Although the basic properties of soils depend on the parent material (or mineral skeleton) and

the influence of vegetation (particularly on organic matter accumulation! I

the edaphic environment is inherently heterogeneous as a result of complex

interactions between many factors. consequently, variation within small areas ~ay create localized sites favourable for growth of a particular plant.

Even though the soil environment has an important influence on plant growth, ultimately it is the genetic ion of a species which determi.nes its habitat limits. Local populations may differ slightly in their tolerance ranges and optima for plant growth (Clausen et al. 1948),

The balance between nutrient requirements of a species and the amounts available in the soil may be crucial for plant growth. The complexity of the soil system does not allow accurate determinations of nutrient availability (see Rorison 1969). However, plants themselves are often used as indicators of soil nutrient status (e.g. Clarkson 1967, Rorison 1967).

By adding various combinations of nutrients to natural soils and comparing 83

the resultant growth with that when no nutrients are added, the effect of soil fertility, especial with respect to those nutrients that are

limiting, can be assessed. Results from such experiments have been used to determine how plant distributions are influenced by soil nutrient

status (CLime and Curtis 1976 1 Rorison 1960a, '.Hllis 1963).

The relative growth rate (R) of specles in potentially productive, standardized conditions is also important since the relative growth rate is thought to be of adaptive significance in nature (Grime 1979) . Species with high R values are predominant in productive habitats, whereas unpro ductive habitats characteristically have species with low R values (Grime and Hunt 1975).

Therefore this chapter examines the comparative growth on different soils of the five Acaena species from two geographical distinct sets of populations. The effect of soil nutrient availabil on growth is examined on natural soils and the relative growth rates are assessed for each species.

5 • 2 MATERIALS AND ME'rHODS

5.2.1

The use of cuttings provided a rapid means of obtaining a large nwnber of genetically similar plants of all five Acaena simultaneously. Considerable success was achieved in rooting cuttings which

\",ere subsequently used in experiments to investigate growth on different soils. Stock plants were collected from the two study sites: Porters

Pass on 13.11. 79 and from the Amuri Basin on 13.12.79. These were grown in a 2:1 sand/loam mixture in boxes in a greenhouse at Christchurch.

Cuttings were taken by exc young shoots with a razor blade just below the second node. These were placed in black plastic polythene pots containing 250 m! water and supported a layer (approximately 1.5 em) 4

of polystyrene beads (3-5 mm diameter) . The use of floating polystyrene

beads allmved the bases of cuttings to remain inunersed in the water even

when the water level altered. Glass panes were placed over the pots to

reduce

After 2-3 weeks, 3-4 root primordia had developed from the nodes,

at which uniformly rooted cuttings wen.! selected for experimental purposes.

5.2.2 Growth on different Is

In order to compare the response of each species to soil quality, rooted cuttings of the five Acaena species from both Porters Pass and

Amuri were grown on three different soils from Porters Pass and potting mix (Appendix II) . Natural soils (top 10 em) were collected in large polythene from three sites at Porters Pass~ a streamside site gravel), a scrub-tussock grassland site (yellow brown earth) and 2.n erosion embankment (fine gravel). Large stones greater than 19 nun were excluded from the soils, as these would have occupied considerable space in growth containers. Descriptions of these soils have been given in section 2.2.2.

Single cuttings were out into 5x5 cm white tic pots containing approximately 200 of soil in triplicate. These were grown in a greenhouse with natural daylength and light intensities for February-April 1980 and watered as required. The experiment commenced on the 12.2.80 with o the plants be harvested after 11 weeks, dried (95-100 C for 48 h) and weighed to 0.0005 g.

5.2.3 Growth in relation to soil

The response to natural soil nutrient status was examined by growing rooted cuttings on natural soils to which nutrient solutions of known constitution were added. The five Acaena species from Porters Pass were 3 ' grown in 5x5 cm white plastic pots containing 200 cm of natural soil from

Porters Pass (section 2.2.2) in triplicate. Nutrient treatments (100 m£) 85

were added at weekly intervals throughout the experimental period and

watered as required between these nutrient solution applications.

The treatments included solutions deficient in the four major

elements necessary for plant growth: nitrogen, phosphorus, potassium and

sulphur, as well as a complete nutrient treatment and a control of no

nutrient treatment. The composition of nutrient treatments was based on

that of Hewitt (1966, Tables 40, 41). Each salt was made up as a concen-

trated stock solution from which fresh culture solutions were prepared

prior to each application (Table 5.1).

Using the Aaaerla species themselves allows determination of whether

nutrient availability is limiting their growth. However, because plants

are usually adapted to the conditions of their habitats, the overall nut-

rient status of the soil may be masked, especially if they are adapted to

low nutrient ies. Therefore a bioassay was carried out on the

natural soils from Porters Pass using Agrostis tenui.s Sibth. This grass

was chosen because it is abundant on low fertility soils and is common in

the communities at Porters Pass. It is also known to respond to nutrient

addition (Bradshaw et al. 1960, 1964).

The experimental design was essentially' similar to the examination of growth in response to nutrient addition for the Acaena species, except

that commercial seed of A. tenu,:s was surface sown in 5x5 cm s, contain- 3 ing approximately 200 cm natural soil on 2.10.80, and given initial nut-

rient treatments (100 mhs), according to Table 5.1. Seedlings were thinned to 4 per pot after 5 weeks when weekly addition of nutrient treatments commenced. Plants were harvested after a total of 13 weeks, dried (95- loooe for 48 h) and weighed to the nearest 0.0005 g. 86

TABLE 5.1 THE COMPOSITION OF MINERlI"L NUTRIENT TREATMENTS.

-, Volume of stock solution (mn per litre of nutrient treatment Stock Compound (gZ 1) '1' r e a t m e n t s -N -p -K -s Complete

t,jacronutl'ients

-~,-

KNO 20.2 10 - 10 10 3 32.8 - 10 10 10 10 Ca(N03 )2 NaH2P04·2H2 ° 20.8 10 - 10 10 10 1-1g50 4' 7H2 0 36.8 10 10 10 - 10

KC1 ! 29.8 10 - - -

(CH COO)2ca 63.3 10 - i 3 NaCl 7.7 10 - -

MgC1 14.3 - - - 10 2 NaN0 3.4 - 10 3

Micronutrients

Fe (EDTA) 3.35 2.5 2.5 2.5 2.5 2.5

MnS0 ,4H O 2.23 1 1 1 1 1 4 2 znS0 ·7H O 0.29 1 1 1 1 1 4 2 cuS0 ·5H O 0.25 1 1 1 1 1 4 2 H B0 3.10 1 1 1 1 1 j 3 Na Mo0 ,2H O 0.12 1 1 1 1 1 2 4 2 NaCl 5.85 1 I 1 1 1 1

0.053 1 1 1 1 1 CoSO 4 .7H 2 ° i 7

5.2.4 Relative rates

The relative growth rate of each Acaerta species \vas estimated using

the approach of Grime and Hunt (1975). This involved growing seedlings

in sand/solution cultures under controlled conditions and calculating the

increase in dry matter between successive harvests. The level and supply

of mineral nutrients ,.;as in r"xcess of that probably ed by Acaena

plants 'in the field. However,there is some evidence to suggest that

species normally considered to be unproductive, grow faster in productive

monocultures than in conditions similar to those of their natural habitat

(Parsons 1968, Rarison 1968) .

Seeds were germinated on moistened filter paper 1n dishes d.t

r"oom temperature, as outlined in section 3.2. On the basis of g,~rmination

trials (Chapter 3), it was possible to stagger the sowing of each species

to allow simultaneous peaks in their germination. Unfortunately, only a

few seed of A. inermis germinated at the beginning of the experimental period. Therefore only 3 replicates were used. For the other 4 species,

10 nated seeds were pricked out, one per container. The com::.ainers were made up from 6.5 x 5.5 cm white polythene tubing cut into 25 cm lengths, with fine nylon gauze over one end ( 5.1) Each pot contained 3 500 cm of fine white sand (obtained from Fletcher Merchants Ltd, Riccarton)

To prevent interference from neighbouring shoots, the container walls extended 12 cm above the sand surface. The containers were supported an open grid which allowed free drainage from each container and ensured

~hat any excess nutrient solution did not become concentrated or contact dny other container. Each container was watered with 20 m~ of nutrient solution (Table 5.1 'complete' nutrient solution) on alternate days. 88

lights 5.3 cm from sand surface

seedling

container 3 500 em sand 12 cm

nylon gauze grille

tray

to waste

Figure 5.1 Verticle section a seedling container.

The containers were randomised in in a Sherer eEL 8 growth

cabinet with an 18 h 6 h night The 1 source was

provided by 8 110 watt fluorescent tubes and 5 incandescent bulbs which -2 1 gave a 1 intensity of 150 microeinsteins m sec at sand level.

0 was controlled at 20± 2 C the day and IS± at night,

with humid maintained above 70%. Harvests were made, one from each pair after 2 and 5 weeks, when seedlings were washed, dried (48 h at 95-

o 100 C) and then weighed to the nearest 0.00005 g.

It is possible that some seedlings suffered setbacks, especially from disturbance during the ication of nutrient solution. Although a crust of a developed on the sand surface in some pots after approximately 2 weeks, it helped to prevent sand d which tended to occur when were 89

5.3 RESULTS AND ANALYSIS

5.3.1 Growth on different soils

The mean growth values (dry weight) for each species when grown

on natural soils and potting mix are given in Table 5.2 (a). '1'he data 2 were transformed to log (dry gxlO ) to equate the variances before e statistical It appears that all five species from both popu-

lations, i.e. Amuri and Porters Pass, have different responses to the 4 different soils (Table 5.2(b)). Generally, the s from Porters Pass grew better than those from Amuri (except A. 9 Presumably this

is due to the Porters Pass being better to their natural soils. Consequently only the results for the Porters Pass plants will be considered in further detail.

A. caesiigZauca grew significantly better on brown earth than on the other soils and hardly grew at allan mix. The other species also had difficulty gett established on mix as shown by the number of s that died (see I + I Table 5.2(a)). It is interes that although A. lauca, A. and A. profundeinc'isa grew on potting mix, these three species all grew best on yellow brown earth.

In contrast, A. and A.• showed growth on coarse TABLE 5.2 la) MEAN GROWTH CUTTINGS PORTERS PASS AND POTTING MIX.

ANOVA

(a)

S 0 i 1 T Y P e ies r--' A Amuri . Yellow Brown .. Fl.ne Gravel h Pottlng MlX p Porters Pass Eart

-0.62 2.26 1. -4. P 2.65 1.39 3.91 -4.

+ + A. A 2.33 1.87 1. 91 3.29 + P 3.13 2.73 2.43 3.57

A. A 1. 61 1.47 2.3') 3 + P 2.15 0.83 1.69 1. 68

A. inennis A 1. 35 1.84 2.49 0.62 P 3.33 3.00 4.05 1.8

A 1.28 1.39 1.91 2.68 3.32 2.57 4.26 1. 90

L.S.D. (5%) 0.41 + one died ~. o 91

TABLE 5.2 (Contd)

(b)

Source of Variation df Mean Fa

__• ______M ___ s - .. --~ ---~----.~

Plant Or 1 19.0654 8.83***

Species 4 23.0525 10.67***

Soils 3 14.8058 6.86**

Oriqin x 4 3.9650 1.84 ns

Origin x Soils 3 5.4627 2.53 ns

Species x Soils 12 14.7389 6.82***

x Species x Soils 12 1.1871 0.55 ns

Error 2.1597

a F 0.001(1,71) 11.89 F 0.05(4,71) 2.52 s s

0.05(3,71) 2.75 E' 0.01(3,71) 4.10 s

F 0.001(4,71) 5.24 F 0.001(12,71)=3.26 s s 92

5.3.2 Growth in re to soil fertii

The grm

to nutrient addition together with the growth when no nutrients were added

are presented in . 5.2. The values were transformed to log (dry e 2 weight gxlO ) to equate the variances before statistical analysis. There

were highly significant differences in the ?rowth of Acaep.a species on

different soils and in different nutrient treatments (Table 5.3). Signi-

ficant interactions between and treatments, as well as soils and

treatments complicate the interpretation of these results.

By comparing the growth when a 'complete' nutrient solution is

added with the growth when no nutrients are added in Fig. 5.2, it is

evident that the growth of A, caesiigZauca only increased in response to

nutrient addition on fine gravel. This implies that the growth of A.

caesiigZauca on fine gravel is limited by nutrient availability. The

growth response in other treatments shows that phosphorus/sulphur and

possibly nitrogen availability all lind t growth on fine gravel.

The growth of A. Fiss'istipu was only limited by nutrient avail-

ability on low brown earth. Significantly lower growth when solutions

deficient in potassium or sulphur were added, suggests that the assium

and sulphur availability are limiting growth of A. fissistipula on this

SOlI.

Growth of the other three species (A. gZabY'a, A. inermis and A.

pY'ofundeincisa) is not limited by the nutrient. status of the natural soils

from Porters Pass. However in some cases, growth in the 'complete' treatment was significantly less than in treatments with no nutrient addition,

or when one nutrient was omitted. The growth of algae and some bryophytes

on the soil surfaces to which nutrients had been added, may have competed 93

TABLE 5.3 ANOVA OE' GRO\~"TH OF THE FIVE ACAENA SPECIES IN RESPONSE TO NUTRIENT TREATMENT ON THREE NATURAL SOILS.

of Variation Mean Square

ies 14.5462 16.11***

Soils 46.0041 50.96***

Treatments 4.0029 4.43**

x Soils 0.7850 0.86 ns

Species x Treatments 20 2.1794 2.41**

Soils x Treatments 10 2.4226 2.68**

Species x Soils x Trea tment~s 40 1.2859 1. 42 ns

161 0.9027

a 0.001(4,161) 4.95 E' 0.001(2,161) 7.32 s

F 0.01(5,161) 3.17 0.05(8,161) 2.02 s E' 0.01(20,161) 2.03 0.01(10,161) 2.47 s 0.05(40,161) 1. 50 L.50.=0·49 I L5.D=O·67 I94

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • -N -p -/( -5 [ a -N -p -K -5 [ o -N -p -K -5 [ o

A inermis A profundeincisa L.5.0.=052 I

Figure 5.2 Growth of Acaena species on natural soils in response to nutrient addition. Treatments are given in Table 5.1. + = one plant died.

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • D W ~ • • • fine coarse yellow gravel gra vel brown -N -p -/< -5 [ o -N -p -K -5 [ o earth 95

with the Acaena plants for nutrients and would have altered soil proper-

ties, such as drainage and temperature. Their removal would have upset

the establishment of the Acaena species.

The growth response of Agrostis tenuis seedlings also differed

ficantly on the three soils and between nutrient treatments (Table 5.4).

Nutrient availability limits growth of this species on all three soils from

Porters Pass, as shown by the increased growth in the 'complete' treatment

compared with when no nutrients were added (Fig. 5.3). In particular,

nitrogen and phosphorus limit growth on all three soils, implying that the

levels of these nutrients are low. Potassium supplies limit growth on

coarse gravel and fine gravel, whereas sulphur is limiting on coarse gravel and yellow brown earth.

TABLE 5.4 AN OVA OF GROVlTH OF AGR08TI8 TENUI8 IN RESPONSE TO NUTRIENT TREATMENT ON THREE NATURAL SOILS.

C( Source of Variation df Mean Square F s

Soils 2 2.4240 35.93**

Treatments 5 0.9146 13.55**

Soils x Treatments 10 0.2579 3.82* *

Error 198 0.0675

a F 0.001(2,198) = 4.61 F 0.001(5,198) 3.02 s s F 0.001(10,198) 2.32 s 96

fine coarse ye/{o'w gra vel gra ve I brow n earth

Figure 5.3 Growth of Agrost-is tenu-is on natural soils in response to nutrient addition. Treatments are given in Table 5.1. 97

5.3.3 Growth rate lS

The mean relative growth rate of each species (R) was calcUlated by Fisher's (1920) formula:

R ~ loge W5 - loge W 2 T where 1"1 and W5 are the total plant dry weights at 2 weeks and 5 weeks 2

tively and T is the time interval between harvests (3 weeks).

The values obtained for each species are presented in Table 5.5.

TABLE 5.5 MEAN RELATIVE GROWTH RATES R AND ANOVA.

R Standard deviation

13 1.28

kl. 06 0.94

46 0.17

2 0.13

48 0.23

Variation df Square

Species 4 .4045 0.69 ns

Error 18 .5843

Q n = 3

a F 0.05(4,18) 2.93 s 98

There was no significant difference in mean relative growth rate between the five Acaena species. In a survey of both herbaceous and woody plants of the British flora (a total of 124 species), Grime and

Hunt (1975) obtained mean relative growth rates in the range of 0.22-2.20 -1 -1 9 g week using similar conditions to those in this experiment. They -1 1 considered that values below 1.0 g g week were low and indicative of stress tolerance. The R values obtained in this experiment should not be directly compared with those of Grime and Hunt (1975) because the light intensities were measured in different units. Approximate conversions indicate that those used here are lower, which may account, to some extent, for the extremely low R values. However, even if these K values are doubled, the Acaena species would still be classified as stress tolerators.

5.4 DISCUSSION

'The growth of Acaena. on different soils showed that plants from Amuri differ in their growth response to those from Porters Pass.

Therefore, although a study of a local popUlation provides a basis for examining the ecological tolerances of a species, other popUlations may react differently when grown in identical conditions. Different populations can be genetically adapted to the conditions in which they are growing as shown for populations of Achillea lanulosa and Achillea borea

(Clausen et al. 1948). Adaptation to soil type and altitude has also been shown for several New Zealand popUlations of Rumex acetosella (Harris

1970) . Therefore, ecophysiological responses of a local popUlation cannot necessarily be extrapolated and considered typical for the species 'at

, unless it is a narrow range endemic.

However, the growth responses of the plants from Porters Pass give an indication of the soil conditions which favour each species. The significantly better growth of A. caesiiglauca on yellow brown earth and of A. tipula and A. glabra on coarse reflect their preferences

for these soils in nature (see section 2.2.2). Such preferences may be due to several factors of soil quality involving physical or chemical characteristics.

The variation in response on pott mix may be due to the five species reacting in different ways to soil quality. In this respect, the species which grew best on yellow brown earth (A. caesiig A.

"ineY'lnis and A. profundeincdsa), also grew poorly on potting mix. In contrast

and A. glabY'a, which grew best on coarse grave)., grew satisfactorily on potting mix. However/ an artificial soil medium is unlikely to contain the same sms as natural soils. The presence of endomycorrhizal associations in the roots of all five Acaena specie

(section 2.3. ) may serve to extend t_he volume of soil accessible to the roots in nature. Such associations are recognised as being extrc?me important in the uptake of mineral nutrients, particularly phosphorus

(Sanders et al. 1975). The absence of the associatio'.l- fungi in artificial soils may prove detrimental to the growth of which would otherwise benefit from such associations.

Previous work has shown that country tussock grassland soils in the South Island are deficient in nutrients essential for plant growth

(Williams et al. 1978). In particular, the subalpine soils from Foggy

Peak Ridge (Fig. 2.6) are very strongly leached (base saturation 4-8%), contain poor reserves of available ic phosphorus, have high C:N ratios (ranging from 24 38) / low cation capacities (9.8-16.8 me.%) and low total bases (0.7 me. ) (Molloy 1964). 100

The Agr'08 bioassay of soil nutrient status also indicated

low nitrogen and s levels in all three soil used in this

study and low and sulphur levels on coarse and fine gravel,

This allows an of the amount of nutrients required by each

species. since all species grow naturally on nutrient poor soils, they

must be adapted to grow in infertile habitat::! and therefore have low nut-

rient demands or efficient means of nutrient The presence

of endomycorrhizal associations in field plants (section 2.3.1) would

undoubtedly aid efficient nutrient uptake and their presence may be essen

tial in infertile habitats.

The growth of A. was limited on fine by phos-

and sulphur availabil and A. fissistipula was limited OCl yellow brown earth by potassiwn and availability (Fig. 5.2). The apparent

subtle differences in nutrient requirements of these species seem to limit their growth on different soil Growth of A. A. and A. profundeincisa was not limited by nutrient on ilny of the three soil types (Fig. 5.2). However, other aspects of soil quality may be limiting growth of these species, since A. gZabr'a grew better on coarse and A. ineT'mis and A. pl'ofundeincisa on yellow brown earth,

5.2) .

Low relative growth rates are considered to be of adaptive cance in stress situations (Grime and Hunt 1975), especially when soil

is growth limiting (Bradshaw et al. 1964). Therefore the low r.elative rates of all five Acaena species is evidence that are stress tolerators. Such an adaptation, which allows the species to make modest demands, v/ould have obvious in the unpredictable, relatively subalpine environment. 101

Under stress conditions, slow growing species may be better

adapted to periods when little or no growth occurs (Grime and Hunt 1975).

This is probably because a species with inherently low growth rate is

functioning closer to its optimal level than a rapidly growing species

that may experience a large reduction in yield under the same conditions.

Slow growing species may absorb nutrients in excess of immediate growth

requirements during nutrient flushes. These reserves may be used to

support growth after soil reserves are exhausted (Chapin 1980, Grime 1979).

A slow growth rate would also extend the time that growth can continue on a given nutrient reserve.

Even though there was no significant difference in growth rate between these five IIcaena species (Table 5.5), growth is on in different ways. II. caesiiglauca has a stouter appearance and produces leaflets than the other species (section 2.1). Plants of this species usually occur as individual c1wnps although some and of stolons does occur in damper, shadier places (Plate 2.2). A, fissistipu and

A. profundeincisa are similar in habit, with more slender, branches. A. g produces many small leaves and has stout woody branches which are more erect than the other A. inel~is has small leaflets and a low stature. Its stems branch extensively and root from the nodes to form mats. '1'he ficance of these differences In habit and gross morphology will be discussed in Chapter 7. 102

CHAPTER 6

lNTERF8RENCE RESPONSES ON THREE SOIL TYPES

6.1 INTRODUCTION

Reactions of plants to the biotic co:nponent of their environment is equally as important as their responses to edaphic and climatic factors.

Interference from other plants occurs when two or more plants are close enough in proximity to modify each others growth (Harper 1965), The resultant interactions may lead to co-existence (when the growth of neither species is depres , suppression (when both species growth

ssed) I or subordination (when one species dominate and suppl.-esses the growth of the other es t 1.. 1hich in extreme cases leads to extinction) depending on the of overlap in their requirements, the proximity of individuals and the relative aggressiveness of each component. When a commonly required growth factor is limiting, interactions are like to regulate population numbers (Harper 1977) and may a role in determining the proportional constitution of species in natural communities (de Vries

1949) .

Since the of interference depends on the overlap in require- me~ts, it follows that the closer the requirements of individuals, the greater will be the struggle for existence

"As species of the same genus usually, though by

no means invariablY, some similarity in habits and

constitution, and always in structure, the struggle

will generally be more severe between of the

same genus, when they come inLo competition with each

other, than between species of distinct genera",

(Darwin 1859 p.127). 103

However, interference between plants in nature may be avoided or reduced

if they possess subtle differences in morphology physiology which

allow them to inhabit different habitats within the same acea (Grubb 1977,

Platt and Weis 1977).

The environmental resources for which plants compete are principally

light, water and soil nutrient supplies which are necessary for growth

(Clements et aZ. 1929). If neighbouring plants shade one another, there

may be mutual or one-sided depression of growth due to decreased light

intensities. Similarly, roots of neighboul- ing plants may be competing

for limited nutrient and water Reduced root extension of the

suppressed species, arising from the modified supply of nutrients and light,

may render it far more susceptible to drought. Thus! there may be several

factors for which species are competing- simultaneously. It is extremely difficul t to elucidate those factors important in competition betr..leen

individuals, and this has been achieved in either experimental or field studies. Experiments designed to show that competition is occurring with to a particular requirement! maintain all other factors at optimal or near optimal levels. For example, when competition for light is examined, optimal of water and nutrients are and light proves to have a vital role (e.g. Donald 1961). Similar , competition for any growth requirement may be demonstrated for the same two species by supplying all other factors at optimal levels. This is not

ing since it is axiomatic that when any factor becomes limiting and is required by both species under examination, it becomes the factor for which competition occurs. The complexity of plant interactions has been emphasised by Harper (1977) and Hall (1978), who agree that it is practically sible to separate them into simple effects because interactions bet\'Jeen factors create complications. In discussing competition for space, de Wit (1960 p.1S) goes so far as to say that to subdivide the 104

complex factors in plant interactions into components lS ••••

"not necessary, inaccurate and therefore inadvisable",

these views, there is a considerable amount of literature

based on identifying single or several factors in the competitive complex.

These have shown that the balance between a of species in mixture

can be altered by the addition of a particular nutrient (van den Bergh

1969, Fitter 1976), alteration of the pH (Rorison 1960b), change in level

of the water table (Harper et aZ. 1961), application of water stress

(Milthorpe 1961) or of shading (Aspinall 1960), to name a few. They define

the effects of changing specific environments and strongly emphasise that

the interaction between a pair of species is a function of the environment

in which the interaction occurs. It seems doubtful whether such exper

ments have contributed s ificantly to the understanding of competitive

effects in nature since by single factors, interactions are

ignored. Therefore experimental analyses of interference should examine

the performance of species in response to neighbours, even though it is

tempt to situations in order to demonstrate a mode for inter-

ference.

Yield data from substitutive experiments where density remains

constant, have been used to study competition (see Trenbath 1974) . The

diallel de can be used to make estimates of the competitive abilities

of a number of species simultaneously (Williams 1962, Chalbi 1967, Rousvoal

and Gallais 1973). providing each species competes in the same way with

~ll species being tested, the average tivity will identi those

species that seem to contribute either positively or negatively to the

yields of their associated species. A positive contribution suggests

that a species increases the of the associate species. A negative

contribution suggests that the species interferes with growth of the other

species, 105

The presence of Acaer'.a species mainly in disturbed habitats,

that competition may be preventing their invasion into more

established grassland sites. Therefore, this chapter examines the growth

of the five Acaena species in association with each other and with three

other species, also found at Porters Pass: Agr':Jatis tenuis Sibth. ~ Rumex

Ha Linn. and 'fl'ifol-iwn repens Linn. (section 2.2.4). since the

growth of each species is likely to vary depending on the environmental

conditions, the responses to other plants are examined on three different

soils.

6 . 1'1ATERIALS AND METHODS

A simple de was employed in which the growth of each Aeaena

species in mixed stands was with their growth in monocultures.

Such exper~nents are analogous biome to the diallel desig~s used

population geneticists, where measures of relative aggressiveness of

several genotypes are assessed. Each of the five Acaena species was

grown in all possible combinations with the other four Acaena species as

\"e11 as with Agrostia tenuiB, Rumex acetosella and Trifolium l'epens in a

greenhouse at Christchurch. There were three different combinations of

each species on the three natural soils from Porters Pass (section 2.2.2)

in tr icate; one containing four plants of species i, the second contain-

ing four plants of species j and the third containing two plants of species

i with two of species j. Cuttings of the Acaena species, Rumex acetosella and Trifolium repens were obtained from stock plants which originated from

Porters Pass and maintained in a greenhouse. TheRe were rooted prior to the experiment (for details see section 5.2) . Commercial seeds of Agrostis tenuis were germinated in sand and pricked out 7 weeks after germination when they were approximately 3 cm in height with 2 leaves. Sample cuttings and seedl were dry weighed at the beginning of the experimental period l06

to provide initial dry we Cuttings were planted in 5x5 cm white

plastic pots containing 200 of soil and were watered as required. The experimental period commenced on 10.1.80 with the

temperature maintained above ~'lhole s were harvested after 20 weeks, dried for at least 36 hours at 95- C, and weighed to the nearest

0.0005 g.

6.3 RESULTS AND ANALYSIS

2 The dry weight increase (gxlO ) was transformed to log x to take e into account the effects of differences between species

The biometrical analysis of diallel combination experiments has become rather sophisticated. Most forms are based on the following measurements:

(1 ) The yield per half pot 6f a pure stand of the ith species,

(2) The yield per half pot of a pure stand of the jth species, x ... JJ (3 ) The yield per half pot of the ith species in association with the

jth species,

(4 ) The yield per half pot of the jth species grown in association with

the ith species, j .

These values are used to derive competitive effects, that is the difference between the growth of specie~3 when grown in mixtures and in pure stands.

After transformation, the data was combined into half pot totals for each species, i.e. the total dry weight of two plants for species mixtures and the total dry weight of four ts divided by two for monocultures. The sums of all three replicates and the differences between them for each soil are presented in Table 6.1. Because the interactions between AgY'ostis tenuis~ Rumex acetosella and TY'ifoliwn Y'epens were not of interest in this study they were not examined. Consequently, the analyses of the interactions of these species with the five Acaena species were treated s 107

TABLE 6.1

MOaTl,a 5.31 8.62 7.12 5.1S 7.71 cf1ceiigtauc.a 0.7. 0.25 0.% 0.66 1.54 -0.73 -0.Q9

Aocten.a B.ll 9.73 0.72 9.03 0.70 ,'.40 9.21 f';slJiBtip.Jt.a -0.31 -0.16 0.59 0.30 0.12 2.29 0.55 O.OS

8.2, 6.11 7.49 7.35 0.00 0.23 -0.29 0.12 0.00 -0.51 -0.20

e .08 7.68 9.55 U.15 <1.59 0.99 0.25 0.12 -0.37 0.36 0.01 -1.48 -0.33

Acaena D. SS 6.B7 7.51 0.05 7.65 3.96 [LEtS Pl'o[uI".drin..,tiea -0. JJ -0.25 0.27 0.01 0.37 -0.65 0.')0 0.76

10.31 10.63 0.25 12.56 10.74 10.70 0.62 0.07 -0.04 cO.59 0.17 0.26

4.39 13.19 n.5? 13.63 12.49 12.92 0.16 0.41 -0.23 -0.26 -<1.56 -0.12

11.10 8.20 12.68 12.00 10.49 }0 .. 95

l"~p;mo -1.50 -0.37 0.51 -0.34 -1.01 0.42 ~==c=c=c-=====

(b)

---_... _-_... _--_. Aaaena 0.56 8.26 5.B7 9.20 6.55 6.90 4.84

ca~qiigl.C1lMa 0.00- -{i. 11 -0.21 0.10 -LOS -0.17 -0.61 0.99 ------Aaacr,ll 8.)6 8.17 7.87 I' .68 5.61 4.94 7.43

ri~Bi8t{.pu1.a 0.60 0 •• 0 0.70 -0.27 -2.01 -0.70 o.n

6.03 0.55 7.13 3.99 0.00 7.19 0.21 -0.47 -1.43 -L51 0.00 -0.14 1.35

4.30 6.11 7.74 7.10 6.93 7.96 0.26

0.71 0.09 -0.17 -0.26 0.70 0.27 -O~26 0.10

Acacna 2.B5 6.37 0.11 1.37 7.17 4.16 -0,86 1.73 -0.63 0.05 -0.5a

A{J1"oat{.s B.61 7.9& 6.ao 11.99 6,17 5.90 tet1uh -0.20 o,oe 0.21 1.30 0.90 0.75

6.31 11.42 10.27 5.91 1l.l7 1,34 -0.57 0.59 2.19 -0.71

'fr£[oti"" I1.SS· ij.32 11.98 10.70 il.27 10.04 Z,36 -0.16 -O.ll -LI1 1.07 0.14 108

TABLE 6.1 (Continued)

(el

Aca~kl 5.77 7.24 0.35 J .5~ 7.10 C3.£lfl,l-g'lauca 0.66 -0.32 -0.16 0.13 -0.01 -0.54 -0.06

Acaona 6~06 n.73 8.94 D.06 loll 12.13 6.02 fissietipuk 0.16 -0, II -D. 0;> -0.02 0.65 -0.08 0.64 0.90

4.59 3.95 0.00 3.22 6.01 -1.00 s. 3a -0.B6 0.3a 0.00 0.47 0.32

9.24 6.JO 3.02 6~EI3 0.45 -0,55 -0.10 -0.21 -0.0" -

9.37 a.24 7.12 4.13 -o.so 0.10 0.66 -1.25 0.04

5.36 12.27 12.37 9.28 11.31 11.79 -0.39 0.62 -0.15 1.31 -LU 0.30

6.91 6.,9 10.90 12.43 v.as 11.91

repens -0.47 0.90 l.OS. -O~Ol 1.22 -0.10 .------~------109

TABLE 6.2 ..ANALYSIS OF BETWEEN AND WITHIN MIXED CULTURE POTS AND BETWEEN MONOCULTURE POTS WHEN THE ACAENA SPECIES ARE GROWN WITH ONE ANOTHER AND (a) AGROSTIS TENUIS (b) RUMEX ACETOSELLA (c) TRIFOLIUM REPENS.

.>0 I 1 • ANly.l.ot, SOUrce of Var1.ation df OHr•• Gravel Fine Gravel 'l'el1ov Brown larCh Klltan Squ4re F." Mean Square F: Me.. n $qu.t ... a r:

I ..) lliJ

lliJ

_It.. "," ...,...... pliation. 0.2073 0.25 ... 0.3161 0.91 ... 0.8198 1.02 ... Specl.. 5 0.8093 l.n III 1.U93 5.53· a.5935 3.24 ... Error 10 0.24U 0.3486 0.8009

0» lliJ

_ pot >dUfer""".. Specl•• Mala: Zff.cta 5 1.9361 60 .. 35"· 1.6001 7 .. 02··· 5.9435 126.. 15*·- lnt.eract.t.oD. 10 1.2345 38.48··' 1.4867 6.52·'· 1.2591 26 .. 7)'·· Error 30 0.0121 0.2279 0.0471

tbDOC:Ul tvr. Pot.. ..pll"'tl ...... 0.2067 0.88 no 0.2067 0.118 ... 0.U94 1.05 "' Speci•• 5 1.7156 ' .. 2"· 4.4626 18.,0··· 4.7692 6.0729·· Irroc 10 0.2361 0.2161 0.7853

Ic) IU._ ...,,, ,,",ula IIepl1cet1

.1I

_noc;altW". pot. iIlepU"'U..... 0.0191 0.08 n. 0.24)2 0.78 ... 0.8ll7 1.0l n. Spec 1.. 0.8533 1.0· 3.9145 10.21" 4.7692 5.81·· Error 10 0.2486 0.3128 0.8177 .. '.0.!1SI2.2a) III 1.M F. 0.00119.20) ·4.50 '.0.01(10,30) • 2.98 r. 0.011'.28/ • 3.23 ,.. 0.Q!)l(~.101 .. 5.5) r. 0.0;(1#10') ·4.10

",0.111(5,](1/ • 3.70 F.0.Oll1(10,lO) 111 4.24 r. 0.O5(~,10) • l,n '. CI~OOl'~#".fj) • s." '. 0.00115,10) .11).50 '. 0.(1115.10) • 5,64 110

The analysis chosen closely follows that of Williams (1962) which

assumes that the yield of one species grown in association with another

is made up of two elements: the average of the first species from

all combinations called the "species effect") and the departure from

that average due to interference from the second species (- called the

"associate effect"). This analysis tests the null hypothesis that the

"species effects" and "associate effects" are additive. A departure

from this hypothesis is detected by estimating the interaction between

these two ffects.

rrhe species effects were analysed using the sums of squares from

mixed pot totals and their differences, as well as the sums of squares

from monoculture pot totals (diagonal values in Table 6.la, b, c).

Significant interactions occur when the yields are above or below that

expected from the overall mean of all the species. The between 'J\ixed- pots error (with 28 of freedom) is used for te the differences, species effects between pots and their interactions. The within mixed-pots error (with 30 of freedom) is used for testing the species differences and their interactions, whereas the between monoculture- pots error (with 10 rees of freedom) is used to test the differences between species ,,,hen grown alone. A summary of the analysis for each soil is presented in Table 6.2.

The aim of the analysis, as outlined by Williams (1962) is to quanti the outcome of diallel crosses estimating the relative competitive abilities of each species based on the addit model. However in all cases (Table 6.2), there were highly significant interactions between species. This implies th~t different species compete in different ways and that the null hypothesis of additivity must be ected. There- fore there is no justification for calculating the relative tive III

abili of each species from the mean "associate effects", as outlined by

Ivilliams (1962) t because the "associate effects" are not independent.

The competitive nature of each species varies depending on Ii/hich species were

grown in combination.

When the differences between mixed and monoculture yields are

calculated for each species combination (Api?endix III), individual compari-

sons of the competitive nature of each species can be made. A semi-quan-

titative summary of these values is given in Table 6.3. An aggressive

species (or good competitor) is defined as one which increas8s in yield

at the expense of another. When two species are grown together and both

their yieldS are enhanced with respect to their monoculture yields, a

mutual stimulation has occurred. Conversely, there is a mutual sion

when both species yields are sed. The following generalizations can therefore be made:

(1) A. caesiiglauca could not tolerate interference on coarse

However it \vas aggressive towards '1'rifoliwr1 repens and mutual stimulations occurred with A. glabra. On fine gravel, A. caesiiglauca competed well with A. fissistipula, A. glabra and A. inelwlis, although there were stimu- lating effects when grown in combination with T. Its interference potential on low brown earth is indicated by its aggressive nature towards all species except A. tenuis.

(2) A. f-issistipula has a low interference potential on all three soils.

Mutual stimUlation occurred between A. fissistipula and A. glabra on coarse gravel and on yellow brown earth, and with R. acetosella on yellow brown earth. Mutual depressions were found between A. fissistiputa and T. rep ens on fine gravel and yellow brown earth, and between A. fissistipula and

A. inerrni.s on coarse and fine gravel. ll2

TABLE 6.3 BETNEEN MIXED AND WJNOCULTURE POT ++ difference? 10.0 g. + 1 9 < difference < 10.0 g. -1.0 g < difference < 1.0 g. -LO g < difference < 10.0 g. difference) -10.0 g. See Appendix III for absolute values.

(a) Coarse gravel

tl co (Q tj tl ~ ~ <:.) N .'" N \l) ;:S ~ ~ \l) P." (j ~:'-l ';C\ co 'll N ';C\ 'll CJ :;:., en -N co c'g +~ ';C\ co tl ','> \l) Associates ';C\ ';C\ N co <:.) ~ co co ,.Q ~ ~ ';C\ tl ';C\ \l) (',) tl 'll CJ -!C> N tl ','" N ;;:: N (fJ () '+-. en ';C\ ~ CJ ~ N ;:::: ~n ;:s "!! ~! ~ <.

A. + + A. fisBist'ipula + A. glabra + + ++ A. inerr7lis ++ + A. profwuieincisa + Agrostis tenuis Rumex acetose l Trifoliwn repens ++

(b) Fine gravel

A. caesiiglauca + + ++ + A. tipula A. glabra A. inermis + + 1- + A. profundeincisa + + + + Agrostis tenuis + ++ Humex acetosella Trifolium l'epenB ++ ++ +

...... ---~.- 113

TABLE 6.3 (Contd)

tj c') tj CJ;) tl .~ CJ;) \'-\ ~ <:.l <:.l .~ t-....~ ~ ~. ;:s ~ cu ~ ~ .~ ~ CJ;) cu j .~ cu cu lJ N en -j4 tr.I -J-'> '+~ Associates ',,\ CJ;) .~ ~ cu .~ .~ tr.I <:J § tr.I CJ;) ~ cK .~ tj .~ cu CJ;) cu lJ -J-'> N tj .~ ~ N u: <:J '+-. .~ n, lJ ~ N ~ ies . , . en ~ ~ ~ ~ ~ ~ ~

A. eaesiiglauca + + ++ + + A. la + ++ A. g + A. inermis ++ + + A. + + ++ Agrostis tenuis + ++ + Rumex acetosella ++ ++ ++ T1'1:foUW71 l'epens ++ 114

(3) On coarse gravel, A. glabra grew better in mixed cultures than in

monocultures, when grown in association with A. and showed

mutual stimulations with A. caesiiglauca:J A. fissistipula and T.

In contrast, it has a low interference·potential on the other two soils.

(4) .4. ineI'lniB has a low interference potential on coarse gravel.

However increased growth, with monoculture , occurred when

A. inerrwis was grm-m Ln association with A. glabra and R. acetoBeZla on

fine and with A. fissistipula and A. glabra on yellow brown earth.

t<1utual stimulations occurred when A. inerrnis was grown with A. pl?ofwuieineisa

on fine and yellow brm-m earth, and T. repena on all three soils.

(5) The interference potential of .4. pl'ofwuieiru]isa varied depending

on the associated s and the soil It appears to be aggressive

toward A. lauca and R. acetose on coarse and towards most

species on the other two soils A. caesiiglauca on yellow brown earth.

(6 ) Agrostis was a competitor to A. inermis on coarse and fine , and to A. caesiiglauca:J A. fissistipula and A. g on yellow brown earth. Root growth of A. tenuia was very extensive and in

some cases the roots had penetrated through the bottom of the pots by the end of the limiting the available space to the roots of the Acaena species.

(7) Rumex acetosella generally has a very low interference potential, although it was aggressive towards A. la and A. inermis on coarse gravel and tovlards A. g on yellow brown earth.

(8 ) Trifolium competed aggressively with A. gZabra on fine t·1utual stimulations occurred with A. inermis on all three soils, as well as with A. g on coarse gravel and A. caesiiglauca on fine 115

6.4 DISCUSSION

There were three outcomes in terms of the yields of species when

grown in association compared with their yields in monoculture.

(1) Both species increased relative to their monoculture yields

(mutual stimulation).

(2) Both species we.re depressed (mutual depression) .

(3) An increase in growth of one species occurred at the expense of

the other species (compensation).

6.4.1 stimulation

Mutual stimulation implies that either the two species are co-oper

ative or synergistic, or together are less restrained than either component

is in monoculture. This type of response is 1 to arise when there

is nutritional complimentation between species, such as when a legume is

associated with a non- leguminous plant. In this respect, there were

five examples of mutual stimulation bet\>Jeen T. and the Acaena species.

However I there were also consistent mutual increases between A. ·inerrm:s

and A. pY'ofundeincl,sa on fine gravel and yellOW brown earth and between

A. fissis la and A. glabra on coarse gravel and yellow brown earth.

Over yielding of species mixtures compared with monoculture yields in non

legume associations appears to be uncommon (Trenbath 1974) and only occurred

in 6 out of 60 combinations in this experiment. Other cases of mutual

stimulation have been by Whittington and O'Brien (1968) and Harper

(1965) . A complicating factor, which has not been considered in experimental work to date, is that observed mutual increases in species mixtures may merely be a reflection of the depression of growth in monocultures due to int.raspecific competitive effects. If competition is more intense than the competition between two different species (which is highly probable because the requirements of plants of the same species 116

are closer than those of different species), then the species in mixtures

will show increased with respect to their monoculture and

therefore give the appearance of mutual stimulation. This may explain

some of the apparent mutual increases observed in this experiment.

Mutual decreases in growth would occur when ion is intense

and neither species has an ability to an over the other.

Each species may restrict the yield of the other physically (in terms of

competition for space) or biochemically (if toxic exudates are invo

The latter is not a competitive effect in the sense of the struggle between

two individuals for the same resource, but is a mechanism which could

explain the observed responses. Mutual decreases in growth occurred

between A. la and T. repens on fine gravel and yellow brown earth!

and between A. f-issistipu and A. on coarse gravel and fine gravel.

However the mechanism of these interactions can only be tive.

6.4.3 increases decreases

When one species is a better competitor than another, it tends to

increase in yield at the expense of the subordinate species, whose growth

is ssed. This type of response was the most common in this experiment

(34 out of 75 possible combinations).

Generally, a higher yielding species in monoculture would be expected to be the aggressor when grown with a lower yielding species (Trenbath 1974).

A higher can be related to the ability of a plant to secure its essential requirements more The associated faster growth may allow it to deve a larger leaf surface area to obtain light and a larger root surface to absorb nutrients and water. It may then overshadow the subordinate species and depress its growth. However the converse is also known (Gustaffson 1951) . This effect, called the Montgomery effect, may 117

arise if the species differ in their ability to exploit the environment.

When the factor for which they are competing is limiting, the lower yield

ing species in monoculture may be the more efficient in obta lower

amounts of the limit factor, and appear to ss the growth of the

other. In this respect, the yield of A. fiss tiptl in monoculture was

grea ter than the other spec ies, ye t A. fiss'i stipu La could no t compe te

against them. This suggests that A. fissistipu is less conservative

in its consumption of resources than the other species.

6.4.4 Comments on the

In some models of analysis, it is assumed that the increase in

growth one species is the same as the decrease in the other

1965), or ,that the increase in proportion to the monoculture is the

same as the proportional decrease of the associate species (Chalbi 1967,

and Caput.a 1970, McGilchrist and Trenbath 1971). This was not

always the case in this experiment. other outcomes, such as mutual stim-

u1ations and mutual ssions indicate that interactions/besides com-

increases and decreases, are possible.

The analysis of the interaction between species using pot cultures

is bound to be a simplification of those arising in nature. The outcome

of competition varies depending on the growing conditions (Sakai 1961).

In different environments, different characters become important, or at

least the balance of importance changes among the characters. One species may be favoured in one set of conditions, whereas changes in the

environment may the balance to favour another species. The responses of the five Acaena species have been examined only with respect to soil

ity. No doubt changes in other variables may produce equally different outcomes. 118

The behaviour of neighbours is also likely to depend on the stage in the life history of the component species. Comparisons between were restricted in this study to the vegetative stage. Nevertheless, comparisons of speci yields in mixturE:!s and monocul tures has indica ted that the Acaena: species differ in their response to interference from other plants. 119

CHAPTER 7

CONCLUDING DISCUSSION

Hany aspects of the l'esults obtained in this study have been

discussed in the relevant chapters. The aim of this chapter is to present

an overview of the findings by summarising the factors important to the

ecology of the five species.

F~ach species (except A. pY'of'undeincisa) has a distinct habitat type

preference within the subalpine tussock grassland site at :?orters Pass

(Table 2.2). The comparative experimental approach used in this study

has shown how the Acaena species are adapted to these habitats and how

factors of the environment (i.e. climatic, edaphic and/or biotic) influence

their distributions.

to the environment

Germination responses indicate that germination would be restricted

to late spring when soil temperatures and soil water conditions would be

sufficient to sustain growth of at least some seedlings. The high ,vater

requirement for germination in A. caesiiglauca3 A. j'issistipuZa.J A. glabl'a

and A. pl'oj'undeincisa would limit germination to moist habitats where

water is abundant for several weeks at a time. These four species also

require moist conditions for seedling growth (Table 4.1). Therefore seed-

ling establishment would be restricted to moister sites which accounts for

their predominance in moister gullies at Porters Pass. Their deep, extensive, woody root systems provide the opportunity for mature plants

to extract water from deeper soil layers, thereby overcoming drought effects when the upper soil horizons dry out. The ability of

A. b~ermis leaves to withstand substantial water loss compared with other 120

species (section 4.3.2) 1S reflected by its presence in drier sites.

The branching habit, low stature and small leaves of A. ineY'l7lis, would

prevent excessive water loss by reducing the leaf area exposed to wind.

High wind velocities are frequent in the subalpine environment

(Fisher 1952). Adaptations to withstand wind are particularly evident

in A. glabra. Woody stems and coriaceous leaves in this species help

minimize damage from wind and moving debris. Its more upright stature,

compared with the other species, presents its seed heads to the wind,

which 1S the most important vector responsible for its seed dispersal.

Seeds of the other species are adapted for animal dispersal, but wind

and streams may also be important in transporting their seeds.

The promotion of germination by 1 in all five s suggests

that germination would be more successful 1n disturbed habitats or bare

sites where there is little shade from other plants. Therefore seed

germination in these Acaena species would be favoured by ic erosion

processes, characteristic of the soils at Porters Pass (Molloy 1963) .

All five Acaena species develop extensive cuticular wax structures

(Plates 4.1 and 4.2). These structures, together with hairs on leaf

surfaces (espec on A. caesiiglauca and A. profundeincisa), promote

light reflection and prevent excessive increases in leaf temperatures (Pearman 1966).

A bioassay (using Agrostis ) of the nutrient status of natural soils from Porters Pass showed that they are depauperate in essential plant nutrients (section 5.3.2). Since there was relatively little growth response of the Acaena species when nutrients were added to these soils, it is concluded that they are adapted to relatively low soil nutrient availabilities. Perhaps they take up nutrients in excess of their immediate requirements during nutrient flushes and use these rese.rves during periods of exceptionally low nutrient availability, Perennial

roots would serve as important storage organs when leaves die back during

the winter in the subalpine environment. The potential for nutrient

aquisition is increased by the possession of an extensive root system

(section 2.1) and associated mycorrhiza (section 2.3.1). There is also

some evidence that plants with mycorrhiza may be more tolerant of stress

conditions such as drought, or in unstable soils where the hyphae may

bring about soil aggregation (Hayman 1980).

Low relative growth rates (Table 5.5) imply that all five Aaaena

species are stress tolerators (Grime 1979). This strategy enables plants

to withstand rigorous physical conditions such as low nutrient availability,

low temperatures, high wind velocities and possibly drought, all of which are common in the subalpine environment.

the distributions of each

Any factor which limits the growth of a plant will influence its distribution in nature. Depending on the severity and longevity of the growth limiting factor, the relative adaptations of plants will determine the range of habitats in which they can survive, grow and reproduce.

A. caesiiglauca has a distinct preference for grassland habitats but also grows in streamside sites (Table 2.2). The preference for grassland habitats can be attributed to several factors.

Growth was significantly better on yellow brown earth (found in grassland sites) which corresponds with its greater interference potential on this soil (section 6.3). Growth on fine gravel was limited by nutrient availability (Fig. 5.2). This soil predominantly occurs in drier, more open sites from which A. caesiiglauca is generally absent. Its larger 122

leaflet dimensions, compared with the other species (section 2.1), may

llow sufficient light capture to maintain growth in shaded conditions

and hence coexistence in grassland/scrub habitats where neighbouring

plants are generally taller. This may also account for its comparatively

better interference potential than the other Acaena es. However a

large leaf surface area could be disadvantaseous in open habitats as it

provides a surface from which evapo-transpiration can occur.

The leaves of A. caesiiglauca are not as resistant to desiccation as

those of A. inex"rnis and A. profundeincisa (Table 4.2). This, together

with the inabil of seeds to germinate and seeJlings to grow in dry

conditions, suggests that its water requirements exclude it from drier,

more open sites.

The major factor limiting the distribution of A. f'1:ssistipula is water availability, as indicated by its preference for streamside sites

(Table 2.2) and its absence from dry, open habitats. Its leaves are

relatively intolerant to desiccation (Table 4.2) and tend to wilt more

than the other Acaena species when water is lost.

Although A. fissistipula has a low interference potential, growth in sites with a high water availability is probably sufficient to perpet uate its existence in such habitats (see Plate 2.3 for lush growth when water is freely available) . However its lack of interference potential would exclude it from well populated grassland habitats. The soils of grassland sites (yellow brown earth) also limit growth of A. fissistipula due to nutrient availability (F 5.2) • It is interesting that growth was significantly better on coarse gravel, the soil on which it was pre dominantly found at Porters Pass. 123

This species appears to be restricted to scree flabitats (Table 2.2).

Both its response to other plants and its water relations are important in

controlling its distribution.

A. gZ,abl'a generally could not tolerate interference (exc on

coarse gravel), 'which excludes it from sites where other species are abundant

This would explain its restriction to scree habitats where very few other

plants can survive. It has been shown that A. gZabra can be classified as

a 'vlater (sensu Maximov 1931) since its leaves are intolerant of

desiccation ('l'able 4.2) and it has a high stomatal index (Table 4.4) indic

ating a high transpiration rate in nature. This prevents high leaf tem-

peratures by providing an efficient cooling system, which is essEmtial for

survival of A. glabra in the evaporating conditions of screes. The devel-

opment of long, woody roots, which conduct water from supplies in deeper

soil layers makes this possible. Therefore A. gZabra has ed a

compromise between protection of leaves from desiccation and the need to

maintain open stomata for photosynthesis.

A inenwis

Interference from neighbouring plants limits A. inermis to drier

gravel sites at Porters Pass where few other species grow. It is more

physiologically tolerant of water stress, as shown bY.its lower water

content at stomatal closure (Table 4.2). It is therefore able to inhabit

more xeric habitats where there are fine gravels, which would be susceptible

to drought in the upper soil horizons. Since it has a low stomatal index

(Table 4.4) I suggesting a low transpiration rate, and possesses other mor

phological modifications aiding water conservation (section 4.4), this

species can be classified as a 'water saver' (sensu Haximov 1931).

Although the formation of mats would help reduce exposure to wind and hence 124

reduce water loss, its low stature would be disadvantageous in maintaining

photosynthetic activity when shadowed by neighbouring plants. This may

explain its inability to withstand interference and its apparent exclusion

from sites where other, taller species grow, such as grassland/scrub

habitats.

Delayed and sporadic germination of A. inermis, although limiting

its establishment from seed, may result in ed germination over

several years. simultaneous germination increases the probability of

mass seedling mortali if unfavourable conditions suddenly arise after

germination.

This species has no distinct habitat preference. It is relatively

tolerant of water stress (section 4.3.2), grows reasonably well Gn all

soil from Porters Pass and has a high interference potential on.tl::ese

soils ('l'able 6.3). However seed viability and germination rates are low and it has a lower optimum germination temperature compared with the other

species. Failure to establish from seed may be an important factor limit-

ing its abundance at Porters Pass where it reaches its lower altitudinal limit.

In conclusion, although many environmental factors may interact to control the habitat distributions of the five Acaena species at Porters

Pass, it appears that the most important factors are their water relations and their ability to tolerate interference from other plants. 125

ACKNOWLEDGEHENTS

I wish to thank all those who showed an interest in this project and especially those Nho assisted me in clarifying my thoughts. In particular, I am especially grateful to:

Dr. AndreN T. Dobson for supervising this study;

Hilary J. Langer, Bryony M. MacMillan and Margaret J. A.

for valuable discussion and suggestions;

Graham R. Young, the late Frank E. McGregor and Ross K. Wilson

for their technical assistance;

Dr. Neil D. Mitchell for supplying a copy of the Rec

Averaging program;

Dr. Elizabeth Edgar for translation of Bitter's monograph on Acaena;

the Chemical and Mechanical Engineering Departments, University of

Canterbury, the Soil Science, Plant Science and Horticulture

Departments, Lincoln College and Botany Division, D.S.I.R., Lincoln,

for the use of equipment;

to my husband Tony for his enthusiasm, patience and support. 126

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APPENDIX I

Data used in the ordination analysis (section 2.2.4).

Percent abundance of the species in at least 10 quadrats.

Those recorded as present ('+') were transformed to 1 for the analysis. G = grassland, R = streamside, S = scree. 137

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Lf"h.m8

}JoJlM'-tJ 144

APPEND.rX II

mix used in studies

The mixture used was a modification of the John Innes seed compost

recollunended for ne plants by Hammett (19'/3, Appendix B ) . 'fhis consisted of:

2 parts loam,

1 part peat and

2 parts sand, with 1200 g and 600 g dolomite per cubic metre.

between water content and water tension

Samples of the lng mix 100 g) were flooded with water for 24 hand ected to a range of water tensions using a pressure membrane chamber. After equilibration, es were weighed, oven dried o (24 h at 95 - 100 C) and reweighed to determine the water content at known water tensions. This relationship is shown in Figure ILL

Reference

Hanunett, K. R. W. (1973) Plant propagation. Reed, Wellington. 64pp. 145

17~

16-

.~---...- .. -~.~-.~.-.-.------. -0.1 -1 -6 water Tension (Bars)

Figure I1.l The relationship between water content and water tension of potting mix. n = J. 146

APPENDIX III

INTERFERENCE RESPONSES OF THE ACAENA SPECIES

Mean di s between mixed and monocu1ture yiel(3.s/half (n "" 3).

Positive values indicate that the 1d of a species was enhanced when

grown in mixtures compared with its yield in monoculture. Negative

values indicate that the yield of a species was depressed when grown in mixtures.

(a) coarse gravel

Associate

A. caesiiglauca -5.80 4.99 -1.16 -7.12 3.66 0.47 5. A. fissistipula .05 3.20 -4.58 -2.93 -20.15 -10.59 -0. A. glabra .03 8.47 4.39 4.03 -7.64 3.64 11.

A. inermis .04 -6.02 -12.31 68 9. A. profundeincisa .48 -6.40 -3.91 33 o. Agrostis tenuis .48 -0.88 -20.22 RLWlex acetosella .17 6.97 -29.46 Trifolium repens .70 -19.50 36.59 27.45 0.91

(b) fine gravel

4. caesiiglauca 95 3.20 14.42 1. 69 0.99 0.51 4- fissist'ipula .34 -8.61 1. 23 1- glabra -0 .75 -12.02 0.56 L inermis -2 .69 -4.25 3.71 L profundeincisa 6 0.08 191'ostis tenuis 0.05 -4.09 56.84 ?wnex acetoseUa -23.72 -39.25 -60.62 "1'i fo Ziwn rep ens -20.98 18.06 8.26 -19.48 147

(c) ye11mv brown earth

lj tJ) tl tQ lj '~ tJ) N ;;:: N '~ N I\) ;:s ~ (4) Q, Q, ',,\ ~ IJJ I\) .~ I\) (4) N OJ -{.> tQ rtl +-> -B .~ IJJ lj .~ ;;:: (4) Associates .~ .~ N IJJ 'V ~ tJ) tJ) ~ ~ .~ tl .~; I\) tJ) 'B \\l \J +-> N tl .~ N ~ N IJJ ~j