Growth and development of four Themeda triandra populations from southern Africa in response to temperature
B.H. Downing and R.H. Groves Department of Botany, University of Fort Hare, Alice and Division of Plant Industry, C.S.I.R.O., Canberra, Australia
Four populations of the widespread, variable grass Themeda Introduction triandra Forsk., from selected sites in southern Africa with Themeda triandra Forsk. is a variable perennial grass widely different temperature regimes, were grown under controlled distributed in southern Africa. It occurs in both summer and conditions at different day/night temperatures and different durations of low temperature. There were few significant winter rainfall regions and occupies a wide diversity of vege differences between populations in the number of tillers per tation types ranging from Tropical Coastal Forest and Thorn plant formed at different temperatures. Plants from the veld {Type I of Acocks I975) to Themeda-Festuca Alpine coldest site (Sehlabathebe, Lesotho) formed most tillers at Grassland (Type 58 of Acocks I975) at altitudes greater than the lowest temperature. No pattern was apparent in the 2 000 m. The species varies cytologically and morphologically results for time to anthesis in response to temperature. (Gluckman I95I; Chippindall I955). In general in the species, Increasing the time of exposure to low vernalizing temperatures (15/5°) decreased the time to flowering tillers commence growth in spring and some flower in the long consistently only in the population from Frankenwald, near days and warm humid conditions of summer, after which Johannesburg, Transvaal. We conclude that there is seeding occurs. New tillers may be initiated in autumn but evidence for only limited differences in growth and they remain dormant through the cold winter months. This flowering responses of T. triandra populations to variation general phenological pattern may differ between populations, in thermal environments. however, especially with regard to movement of the growing S. Afr. J. Bot. 1985, 51: 350-354 points {Tainton & Booysen I963; Rethman I97I). Vier plantpopulasies van die wydverspreide, varierende The aim of experiments described in this paper was to grassoort Themeda triandra Forsk., van geselekteerde investigate physiological differentiation in four populations groeiplekke met verskillende temperatuurregimes in Suider of the species when subjected to various temperature and Afrika is gekweek onder beheerde toestande teen verskil vernalization treatments in the CSIRO phytotron, Canberra. lende dag/nag-temperature en verskillende periodes van lae The results could then be used to demonstrate the degree of temperature. Daar was min betekenisvolle verskille tussen populasies in die hoeveelheid stingelsuiers per plant parallel evolution shown by the species in southern Africa gevorm teen verskillende temperature. Plante vanaf die relative to that recorded (Groves 1975) for T. australis (R. Br.) koudste plek (Sehlabathebe, Lesotho) het die meeste Stapf, a very similar species widespread in Australia and stingelsuiers teen die laagste temperature gevorm. Die Papua- New Guinea. invloed van temperatuur op die tyd tot antese wys geen waarneembare patroon nie. Deur die tyd van blootstelling Methods aan lae vernalisering-temperature (15/5°) te vermeerder is die Populations tydperk tot blomvorming net in die plantgemeenskap vanaf Frankenwald, Johannesburg, Transvaal verhoudingsgewys Four populations {Table I) were used to study the effects of verminder. Ons lei af dat daar getuienis is vir slegs geringe temperature on growth and development. These populations verskille in die groei- en blomreaksies van verskillende T. occur along a temperature gradient from subtropical condi triandra-bevolkings op wisselings in die termiese omgewing. tions at Hluhluwe on the Natal east coast to alpine at S.-Afr. Tydskr. Plantk. 1985, 51: 350-354
Keywords: Africa, flowering, growth, populations, Themeda, temperature Table 1 Detail of sites from which seeds of four populations of Themeda triandra were collected
Location Lat. Long. Altitude Site (oS) (oE) (m) Collector B.H. Downing Present address: N.S.W. Department of Agriculture, P.O. Box I. Frankenwald, 26° 04' 28° 06' I 500 F. Thatcher 286, Cobar, N.S.W. 2385, Australia Transvaal 2. Hluhluwe, 28° 04' 32° 08' !50 I. Macdonald R.H. Groves* Natal Division of Plant Industry, CSIRO, G.P.O. Box 1600, Canberra, 3. Ukulinga, 29° 40' 29° 22' 660 N. Tainton A.C.T. 2601, Australia Natal *To whom correspondence should be addressed 4. Sehlabathebe, 29° 52' 29° 05' 2400 C. Martin Lesotho Accepted 25 April 1985 S. Afr. J. Bot., 1985, 51(5) 3S1
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20 6 0
~ :J 1§ Hluhluwe Ukulinga Frankenwald Sehlabathebe Figure 1 Mean monthly maximum and minimum temperatures for four stations close to collection sites of Themeda triandra populations. Horizontal bars represent the average period of frost occurrence (mean daily minimum < 0°C). Sehlabathebe in the Drakensberg Mountains at an altitude of than 18/13° grew extremely slowly (see Groves 197S) under 2 400 m. Temperature data close to those existing at each of phytotron conditions. All plants were grown at a 16-h day the four sites are given in Figure 1. Data for Hluhluwe were length (as above). Tiller number was counted weekly up to based on those for Umfolozi Game Reserve, about 1S km week 9, when the stems of some plants began to elongate. to the south; those for Ukulinga from Pietermaritzburg; those Time from sowing to anthesis was recorded for each plant. for Frankenwald from Johannesburg; and those for Sehlaba At anthesis, individual plants were harvested, the number of thebe from Mokhotlong. All sites lie between 26° and 30°S elongating stems counted and the dry weight of leaves, stems latitude; they were so chosen to minimize any differences in (including flowering heads) and roots determined. Plants photoperiodic responses between populations. which had not flowered by day 340 were discarded. The duration of frost (mean daily minimum < 0°) also Seedlings of the same four populations were used to study varies between the sites (Figure 1). Sehlabathebe is colder than the effects of vernalization on time to flowering. Seedlings Mokhotlong and frost is possible on any day of the year. An raised in naturally-lit cabinets at 27/22° and 8-h days were average of eight frosty days per year is expected for given three periods of vernalizing temperatures (IS/ 5°) from Frankenwald; these mostly occur from June to August. Frost week 8; groups of six plants of each population were verna rarely occurs at Ukulinga; if it does it is in July. Frost has lized for 2, 4 and 6 weeks, respectively, and a control group not been recorded at Hluhluwe. remained at 27/ 22°. As soon as the last groups were returned, These four populations were also used to study vernalization temperature was increased to 30!2S0 and daylength increased effects on flowering. to 16 h to optimize the flowering response. To reduce the Voucher specimens of plants representative of each popu possibility of chilling injury during vernalization the following lation are lodged with CSIRO Herbarium Australiense, routine was followed: At 8h30, the 'day' temperature of 1S 0 Canberra and the Botanical Research Institute Herbarium, was given but plants remained in darkness; at 9h00, plants Pretoria. received daylight until at 16h00 daylight was excluded; at 16h30, the 'night' temperature of so was given. Thus during Experimental vernalization the effective daylength was only 7 h. The later The methods used were similar to those described earlier introduction and earlier cessation of light relative to the (Groves 197S), to allow comparison between the two sets of temperature changes was to promote stomatal closure before results. Seeds of each population were germinated on moist and until after the cold period. No signs of chilling injury, filter paper in petri dishes at room temperatures. Approxi such as leaf tip necrosis, were evident on plants given this mately 8- 10 days later, seedlings were planted one per plastic regime. pot (120 mm diameter) filled with 111 vermiculite/perlite and Results for tiller number per plant were transformed to logw placed in a naturally-lit glasshouse maintained at 27/22° (x + 1) before analysis of variance and calculation of LSDs day/night temperature in the Canberra phytotron. Natural (Figure 2). For tiller numbers and total dry weights of plants daylength was supplemented by artificial light of low intensity at anthesis, standard errors of the means were calculated to give a daylength of 16 h. Plants were watered once daily (Table 3). with half-strength nutrient solution and once or twice daily with tap water as required, so that water and nutrient regimes Results should have been optimal. As plants increased in size they Growth and Flowering at Different Temperatures were transplanted to larger pots (22S mm diameter). Generally, tiller number per plant at 9 weeks increased with To study the effects of temperature on growth and flo increasing temperature. For the populations from Hluhluwe wering, five seedlings of each population were moved 8 - 10 and Ukulinga, tiller number increased with temperature up days after sowing to naturally-lit glasshouses maintained at to 36/ 31 o (Figure 2) although not always significantly so for the following temperature regimes: 18/ 13°, 21116°, 27/22°, Ukulinga at the higher temperatures. Tiller number of the 33/28° and 36/31 o. The so differential between day and night Frankenwald plants did not increase significantly above temperatures is standard for the Canberra phytotron (Morse 27/22 o. Tiller number of the Sehlabathebe population, from & Evans 1962). Themeda plants at temperature regimes lower the highest altitude, did not increase significantly between 352 S.-Afr. Tydskr. Plantk., 1985, 51(5) By day 340 when the experiment ceased, no Ukulinga plants had flowered at 18/13 o, only one at 21116°, whilst at 27/22 o 1,5 the time to anthesis was double that of the other populations. Most plants took longer to flower at 33/28° than at 27/22°. An acceleration of time to anthesis occurred at 36/31 o for plants from Ukulinga and Sehlabathebe, but in most cases their subsequent floral development was abnormal and they failed to set viable seed. All populations showed considerable variation in the mean number of days to anthesis (Table 2). Variation was maximal near the temperature extremes, but was small at the optimal 1,0 27/22 o. Least variation ( 14 days) was shown by plants from ;:::- Frankenwald grown at 27/22° and most variation (189 days) + by plants from Sehlabathebe grown at 33/28°. Q; .0 In general, total dry weight per plant at anthesis decreased E ::J c with increasing temperature up to 27/22°; thereafter, total dry Q; -- Hluhluwe weight increased at 33/28° and was reduced at 36/31 o (Table E 3). This pattern is true for all populations except Sehlabathebe ---- Ukulinga Ol 0 between 18/13° and 21/16° and Ukulinga between 21116° _J ·••··••· Frankenwald and 27/22°. The results on total dry weight appear to be in 0,5 part a function of the time to anthesis - the longer the time ---Sehlabathebe taken to flower, generally, the greater the plant weight. Ukulinga plants took the longest time to flower and generally had the highest number of tillers at anthesis. In Hluhluwe plants, the proportion of root weight generally decreased with increasing temperature whilst the proportion of leaves and percentage of elongating stems increased. Patterns in relative dry matter distribution were not easily detectable in plants from other populations. An increase in temperature from 33/28° to 36/31 o led to a decline in the 18/13 21/16 27/22 33/28 Day/Night temperature ("C) percentage of elongating tillers (and an increase of leaf weight) in plants from Ukulinga and Sehlabathebe, whilst Franken Figure 2 Tiller number of 9-week-old plants of four populations of wald plants were relatively unaffected. The percentage of stem Themeda triandra grown at increasing day/night temperatures. LSD weight was greatly reduced in Sehlabathebe plants by this value (P = 0,05) is shown. temperature increase. Vernalization and time to flowering 27/22° and 33/28° but increased significantly between 33/28° Time to anthesis was reduced when plants from Hluhluwe and 36/31 o. Sehlabathebe plants had the most tillers at the and from Frankenwald were exposed to four weeks of vernali lowest and highest temperatures when compared with those zation (Figure 3). By contrast, plants from the coldest site from the other populations. at Sehlabathebe took longer to flower when vernalized, Time from sowing to anthesis decreased as temperature especially in the case of the two-week treatment which delayed increased from 18/13° to 27/22° (Table 2) for plants from anthesis by about 80 days. Plants from Ukulinga required all but Ukulinga. At 27/22° all plants, except those from about 240 days to reach anthesis without vernalization; two Ukulinga, flowered between 89 and 122 days after sowing. weeks of vernalization reduced this time to 130 days, but four weeks of vernalization gave a similar result to the control. Ukulinga plants given six weeks of vernalization were still Table 2 Days from sowing to anthesis of four vegetative at the end of the experimental period of 340 days. populations of Themeda triandra grown at different day/night temperatures. Means and ranges are given Discussion Themeda triandra is a species of predominantly tropical and Day/night Time to anthesis (days) subtropical regions of Africa and south-western Asia. As is Temperature------to be expected from such a distribution, our results show that (0C) Hluhluwe Ukulinga Frankenwald Sehlabathebe the species is able to grow and flower at relatively high 18/13 229 a 215 244 temperatures (up to 36/31 °) and that temperatures of about (209-252) (189-245) (215-319) 18/13° severely limit these processes, as befits a grass with 21/16 !54 132 168 a C4-pathway of photosynthesis. In southern Africa, the (139 -181) (129 -138) (135- 233) 27/22 110 238 96 103 species occurs widely and predominantly in subtropical (103- 122) (222- 248) (89- 103) (89 -118) regions, but it also occurs at altitudes of up to c. 2 500 m 33/28 135 256 127 183 in the Drakensberg of Natal and Lesotho at sites which are (113 -174) (189-311) (96- 139) (103- 292) as cool and the growing season as short as any in southern 36/31 130 169 141 97 Africa. The chosen transect of sites represents a very consi (111-139) (121- 216) (113- !54) (81-113) derable range of thermal environments (Figure 1), all at aNo flowering by day 340 approximately the same latitude (Table 1). The results provide bOnly I plant flowered by day 340 some evidence of adaptation of T. triandra populations to S. Afr. J. Bot., 1985, 51 (5) 353 Table 3 Tiller number, percentage of stems elongating and dry weight of plants of four populations of Themeda triandra harvested at anthesis and grown at a range of day/night temperatures. Dry weight of plant parts shown as a percentage of total dry weight Dry weight distribution Tiller no . Elong. (OJo total) Total dry Day/night ± S.E. stem weight (g) Temp. (0 C) Population mean (%) Leaf Stem Root ± S.E. mean 18/ 13 Hluhluwe 64± 19 58 37 49 14 162±82 Ukulinga a a a a a a Frankenwald 49±8 45 33 39 28 59± 18 Sehlabathebe 144±30 7 59 9 32 61 ±6 21116 Hluhluwe 55±4 52 34 48 18 144±35 Ukulinga 79b lOb Sib 6b 13b sob Frankenwald 44±8 54 27 43 30 52±9 Sehlabathebe 196±45 11 58 26 16 91 ±40 27/22 Hluhluwe 45±9 62 35 52 13 55±4 Ukulinga Ill ±27 74 9 71 20 195 ± 129 Frankenwald 53±7 66 35 52 13 47±5 Sehlabathebe 72± 10 71 39 47 14 43± 15 33/28 Hluhluwe 80± 18 80 47 44 9 122±34 Ukulinga 159±9 85 9 87 4 169± 13 Frankenwald 80± 12 88 46 47 7 144±21 Sehlabathebe 119±35 66 24 70 6 91±21 36/31 Hluhluwe 77±7 79 43 46 II 74±7 Ukulinga 113± 18 44 16 79 5 72±32 Frankenwald 59±9 87 45 50 5 103 ±20 Sehlabathebe 125± 15 21 59 29 12 36±8 aNo flowering by day 340 bOnly I plant flowered by day 340 particular environments. For instance, plants from the coldest however, all populations behaved fairly similarly and the site (Sehlabathebe) (Figure 1) formed significantly more tillers Sehlabathebe population formed the most tillers, even at at the lowest temperature than the other populations from 36/31 o, which is a regime it would never experience naturally. warmer sites (Figure 2). At the higher temperature regimes, We conclude, overall, that there is only limited evidence for growth differences in response to temperature between the different populations. Indeed, the general conclusion for 250 --- Hluhluwe T. australis (Groves 1975) that there was 'little, if any, selection ---- Ukulinga between natural populations for a growth response in relation ...••••• Frankenwald to temperature along an east-west transect of sites all at the I --Sehlabathebe same latitude' also applies generally to T. triandra. I I Increasing temperature decreased the time to flowering for I Hluhluwe, Frankenwald and Sehlabathebe populations up to I I 27/22° (Table 2), which was also the optimum temperature I regime for flowering in T. australis (Groves 1975). We 200 I conclude that there seems to have been no selection for time It was, after all, only in the populations of T. australis from suggested the vernalization regime. To all these people and much higher latitudes that Evans & Knox (1969) found an the collectors listed in Table 1, our thanks. B.H.D. was a obligate requirement for vernalization. Visiting Scientist with CSIRO Division of Plant Industry, The results of these preliminary and limited experiments Canberra, during the course of these experiments. under controlled conditions lead us to conclude that there may have been less selection for physiological responses in T. References triandra than is known for T. australis (Evans & Knox, 1969; ACOCKS, J.P.H. 1975. Veld types of South Africa. Second Groves 1975), although the general lack of selection for growth edition. Mem. bot. Surv. S. Afr. 40: I - 128 . responses to temperature seems to be similar in the two taxa. CHIPPINDALL, L.K.A. 1955. A guide to the identification of Our sampling of sites in southern Africa was necessarily grasses in South Africa. Part I: The Grasses and Pastures of limited and the number of plants we could grow (5 per South Africa, ed . Meredith, D. Central News Agency Ltd. pp. 490 - 2. treatment only) was restricted by insufficient viable seed being EVANS, L.T. & KNOX, R.B. 1969. Environmental control of available to us. Increased replication may have increased the reproduction in Themeda australis. Aust. J. Bot. 17: 375 - 89. physiological significance of the results; wider sampling of GROVES, R.H . 1975. Growth and development of five populations sites, especially from regions of higher or lower latitudes and of Themeda australis in response to temperature. Aust. J. Bot. more aridity, may have increased the ecological significance 23: 951 - 63. of the results. Perhaps the influences of fire and grazing and GLUCKMAN, E. 1951. Cytotaxonomic studies in the species Themeda triandra Forsk. Ph.D. thesis, University of the their interaction have had an overriding effect on the evolution Witwatersrand. of physiological variation in T. triandra in southern Africa. MORSE, R.N. & EVANS, L.T. 1962. Design and development of Accordingly, we have imposed different cutting regimes on CERES - an Australian phytotron. J. Agric. Engng Res. 7: several populations of both T. triandra and T. australis and 128 - 40. shall present those results elsewhere. RETHMAN, N.F.G. 1971. Elevation of shoot apices of two ecotypes of Themeda triandra on the Transvaal highveld. Proc. Grassl. Soc. Sth Afr. 6: 86 - 92. Acknowledgements TAINTON, N.M. & BOOYSEN, P. de V. 1963. The effects of We acknowledge the technical help of the late K. Keraitis, management on apical bud development and seeding in Themeda Ms P.E. Kaye and the phytotron staff. Dr I.F. Wardlaw triandra and Tristachya hispida. S. Afr. J. Agric. Sci. 6: 21 - 30.