The Development of the Tussock of a Clonal Grass Interciencia, Vol

Interciencia ISSN: 0378-1844 [email protected] Asociación Interciencia Venezuela

Feldman, Susana Raquel; Julio Gattuso, Susana; Lewis, Juan Pablo The Development of the Tussock of a Clonal Grass Interciencia, vol. 32, núm. 6, junio, 2007, pp. 399-403 Asociación Interciencia Caracas, Venezuela

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How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative THE DEVELOPMENT OF THE TUSSOCK OF A CLONAL GRASS

Susana Raquel Feldman, Susana Julio Gattuso and Juan Pablo Lewis

SUMMARY

The development of the tussock architecture in Spartina argenti- bearing more than five shoots. All buds are protected from fire nensis Parodi (Poaceae: Chlorideae) is analyzed. The anatomy of by strips of lignified tissues. Monk tonsure-like gaps are regular- the rhizomes and the position of the buds that continue growth af- ly produced in the life cycle of the plant; their development be- ter disturbances such as fire are described, using pot grown plants gins when the plant has at least ten shoots and the growth of the and field collected adult plants. The plant exhibits a phalanx type rhizomes determines the future rays of the tussock. Environmental of growth and begins to differentiate sympodial rhizomes after factors only allow the central gap to be seen.

RESUMEN

Se analiza el desarrollo de la arquitectura de las macollas de más vástagos aéreos. Todas las yemas están protegidas contra el Spartina argentinensis Parodi (Poaceae: Chlorideae). Utilizando fuego por bandas de tejidos lignificados. Las tonsuras de mon- plantas crecidas en potes y plantas recogidas en campo, se des- je se producen regularmente a lo largo del ciclo de vida de la cribió la anatomía de los rizomas y la posición de las yemas, planta, su desarrollo comienza cuando la planta tiene al menos que continúan el crecimiento después de disturbios tales como el diez vástagos aéreos y el crecimiento de los rizomas determina fuego. La planta presenta un crecimiento tipo falange y comien- los futuros rayos de las macollas. Los factores ambientales solo za a diferenciar rizomas simpodiales después de emitir cinco o permiten que se visualice ese claro o tonsura de monje.

Introduction has been described in many Agropyron spicatum and A. argentinensis and intersti- species by several authors desertorum) and postulated tial species such as Chloris Clonal plants are charac- (Ruiz Leal, 1959; Lewis et that it can be the result of halophyla, C. ciliata, Dis- terized by bearing modules al., 1990, 2001; Danin and three mechanisms: over- tichlis spicata, Sesuvium that can achieve independent Orshan 1995; Wikberg and grazing, undergrazing or se- portulacastrum, Heliotro- life, giving rise to a new in- Mucina, 2002) but it has nescence. There is no solid pium curassavicum, Pluchea dividual or ramet according not been established if it is evidence of any of these hy- sagittalis, Salicornia ambig- to different growth patterns. due to environmental factors potheses. ua, Verbena litoralis, etc. Therefore, grasses can be or if it is inherent to the Spartina argentinensis The tussocks of S. ar- considered as modular or- growth pattern of the plant, Parodi (Poaceae) is the gentinensis can be >1m in ganisms where the shoots are as thought by Adachi et al. dominant species of the tall diameter, and very often the structural units (Harper, (1996), who claimed that at grasslands of depressed ar- large central gaps can be 1977) and their shape or least the forb of Reynou- eas of the Chaco-Pampean seen. They have been called architecture is determined tria japonica it was brought plain of north-central Argen- monk’s tonsure-like gaps mainly by the angles formed about by the growth pattern tina (Cabrera and Willink, (MTLG) and it has been by the shoots that appear of the rhizome system. 1973; Lewis et al., 1990). proposed that they could successively (Godin et al., Strickland (1983) de- The communities of S. ar- be the result of tussock de- 1999; Godin, 2000). scribed this phenomenon in gentinensis thrive on hy- velopment, or disturbance In some cases, as the grasses from North Ameri- dro-halomorphic soils with such as fire (Lewis et al., plant grows radially the ca (Oryzopsis hymenoides, high Na concentration, and 2001). The MTLG increase central part of the plant Festuca idahoensis, Stipa pH ~8, and have an almost in size with time and the dies out. This phenomenon spp., Muhlenbergia torreyii, unspecific matrix with S. ring of shoots around them

KEYWORDS / Disturbance / Fire / Grasslands / Ontogeny / Spartina argentinensis / Received: 11/09/2006. Modified: 03/05/2007. Accepted: 03/20/2007.

Susana Raquel Feldman. Agro- de Investigaciones of the UNR Susana Julio Gattuso. Pharmacist Botanics. University of Cam- nomic Engineer, Universidad (CIURN). Address: Univer- and Doctor, UNR, Argentina. bridge. UK. Professor, UNR Nacional de Rosario (UNR), sidad Nacional de Rosario, Professor, UNR, Argentina. Researcher, CONICET, Ar- Argentina. Doctor Biological CC 14, S2125ZAA Zavalla, Juan Pablo Lewis. Agronomic gentina. Sciences, Universidad Nacional Argentina. e-mail: sfeldman@ Engineer, Universidad de Bue- de Córdoba, Argentina. Profes- unr.edu.ar nos Aires, Argentina. Ph.D. en sor, UNR, Researcher Consejo

JUN 2007, VOL. 32 Nº 6 0378-1844/07/06/399-05 $ 3.00/0 399 RESUMO

Analisa-se o desenvolvimento da arquitetura dos maços de mais caules aéreos. Todas as gemas estão protegidas contra o Spartina argentinensis Parodi (Poaceae: Chlorideae). Utilizan- fogo por bandas de tecidos lignificados. As tonsuras de monge do plantas crescidas em potes e plantas recolhidas em campo, se produzem regularmente ao longo do ciclo da vida da planta, se descreveu a anatomia dos rizomas e a posição das gemas, seu desenvolvimento começa quando a planta tem pelo menos que continuam o crescimento depois de distúrbios tais como o dez caules aéreos e o crescimento dos rizomas determina os fogo. A planta apresenta um crescimento tipo falange e come- futuros diâmetros dos maços. Os fatores ambientais somente ça a diferenciar rizomas simpodiais depois de emitir cinco ou permitem que se visualize esse claro ou tonsura de monge.

eventually breaks down in growth after fire, and 3) to wax. Cross and longitudi- Rhizome anatomy several segments, some of determine what mechanisms nal sections (18-20µm thick) which may give rise to new trigger MTLG (Lewis et al., were obtained and colored Portions of the rhizome tussocks. Therefore, their 1990, 2001) development. with safranine-fast green from tussocks >20cm in di- development may be very (Dizeo de Strittmater, 1979). ameter were taken from the significant for the vegetative Material and Methods Drawings were made using field and placed during 48h regeneration of the grassland a Wild TYP 308700 stereo- in 10% ethilendiamine (Carl matrix, in a similar way as Morphological and ana- microscope equipped with a quist, 1982). Then they were the directional growth of tomical observations and drawing device. The pres- rinsed under running water, a clonal bromeliad species studies were made on seed- ence of lignin in the sheath dehydrated and colored in in the Brazilian restinga lings obtained from seeds of non-elongated shoots of the same way as indicated community (Sampaio et al., (caryopses) or from adult seedlings with no more than above. Starch presence was 2004). plants of the Federico Wil- three aerial shoots was de- determined by iodine-io- Fire is a common dis dermuth Reserve, Argentina termined with the fluoroglu- dite test using plants with turbance in American grass- (31º57’S, 61º23’W). The Re- cine test (Ruzin, 1999). seven emerged shoots. In all lands, even before European serve is representative of schematic anatomical repre- colonization (Uresk et al., the halophylous grasslands Tussock ontogeny sentations Metcalfe (1960) 1980; Knapp, 1985; Eskuche, of the area and was estab- symbols were used. 1992). Large biomass ac- lished in 1988, cattle being The architecture analy- cumulation is a common excluded from the area since sis was made by measur- Structure analysis of adult feature in S. argentinensis 1991. Adult plants randomly ing the angles determined plants and their response grasslands (Feldman and collected from the Reserve by the first and successive to disturbance Lewis, 2005), so fires are were from an area free of shoots corresponding to frequent at the end of winter fire at least for the last 15 eight seedlings. Seedlings Plants corresponding to or during dry summers. years. Seedlings were grown grown in pots and with 3 to different ranges of basal Although there are sev- in 20cm diameter pots filled 13 emerged shoots were cut diameters (7-15cm, n=10; eral studies on the morphol- with Reserve soil and main- at 5cm from the base and 25-30cm, n= 6; and 40- ogy of different species of tained outdoors from March kept vertically below a glass 45cm, n= 3) were randomly Spartina (Sutherland, 1916; (autumn) onwards at the panel mounted on a 10cm selected from the popula- Caldwell, 1957; Metcalfe, Facultad de Ciencias Agra high wooden frame, so that tion, and leaves and roots 1960; Levering and Thom- rias gardens, 150km SE the points corresponding to were removed leaving the son, 1972; Anderson, 1974; from the Reserve. Botani- each shoot could be marked rhizomes exposed. Diam- Walsh, 1990; Perazzolo and cal terms are according to on a transparent sheet. The eters of tussocks and the Pinheiro, 1991), there are Hickey and Clive (2000). angles were measured ac- central area of each plant neither morphological nor cording to a Cartesian co- were measured. The sector anatomical descriptions cor- Rhizome ontogeny ordinate system, with the bearing shoots with all its responding to S. argentinen- origin passing through the senescent leaves was con- sis. After fire or clipping, Seedlings with 3, 4 and 6 first shoot, in such a way sidered the central area. The gaps in large tussocks of S. shoots were collected in or- that the angles determined ratio between the central argentinensis were visible der to determine from what by the abscissa axis and the area and tussock diameters (Feldman et al., 2004) but stage they begin to develop segments of shoots 1-2 and was calculated, and differ- there is no evidence if the rhizomes, when lignified 1-3, clockwise and counter ences among groups were MTLG were the result of cell strata are differentiated clockwise respectively, were assessed using ANOVA and disturbance or otherwise; and the characteristic archi- equal. Angles of each shoot Duncan test. Bud viability it is a characteristic of the tecture of the plant set up. in relation to the abscissa of the nearest live shoot to plant ontogeny. The objec- The 10 basal mm were cut were determined relating the removed central area tives of this paper are 1) off, removing the roots, and points corresponding to each (n=6 per plant) was deter- to analyze the plant archi- the remaining portions were shoot to the first shoot. The mined by incubating them tecture (sensu Godin et al., put in a 30% hydrofluoric cross section of a plant with during 6h in the dark at 1999; Perreta and Vegetti, acid solution during six days six primary shoots was out- 28ºC in 1% phenyl-tetrazo- 2005) of S. argentinensis, 2) (Ruzin, 1999). Then, they lined showing the position lium chlorine (Busso et al., to describe the anatomy of were rinsed under running of the primary and second- 1993). Similar plant series the rhizomes and the posi- water, dehydrated in alco- ary shoots at 5cm from the as stated above (n=5 in the tion of the buds that restart hols and included in paraffin base. first two categories and n=3

400 JUN 2007, VOL. 32 Nº 6 in the third one) of aerial shoots. were placed on All transversal sec- trays with humid tions of the sheaths sand and the aerial bases tinted with part up to 3-5cm fluoroglucine were from the base was wine-red; therefore, removed, in order their cell walls to analyze the re- were already ligni- sprout pattern after fied, although seed- clipping. lings were only 2-3 months old. Results Tussock ontogeny Figure 1. Cross section of the base of a 4.5 month-old seed- Rhizome ontogeny ling of S. argentinensis with roots in transverse section. No rhizome is present. The second and When the first third shoots grew two leaves start at a 29 ±14º angle to age, two new in relation to the Figure 4. Cross section of a tus- shoots emerge in vertical plane of sock of S. argentinensis with primary (1-6) and higher order an alternate way, the first one, pro- shoots (section at 5cm from the very near to each jecting them clock- ground). Bigger circles mark the other and usually wise and counter position of the primary shoots, enveloped by the clockwise, respec- the numbers indicate the order of sheath. Adventi- tively, on the hori- emergence, and secondary shoots tious roots origi- zontal plane of the have as first digit the number of nate at the basis developing tussock. the primary shoot where they grew. Arrows show growth di- of these shoots, as Successive shoots rection. in the main shoot, emerged in an al- when seedlings are ternate way, at each 2-3 months-old; the side of the first start growth in the arrows first leaf is 4-5cm shoot, turning away direction (Figure 3b). long and may have from it and forming The diagram of the grow- started to age. a circumference on ing tussock’s base and the The cross sec- the tussock hori- circumference formed by Figure 2. Cross section of the base of a 6 month-old seedling all the shoots (6 primary tion at the base of of S. argentinensis with six shoots and two roots in transverse zontal plane. The a 25.8cm high, 4.5 sections, showing the rhizome in longitudinal section. measured angles and 20 of higher order) is month-old plant were progressive- presented in Figure 4. Each with four shoots is ly larger. Usually, emerged shoot produced new presented in Figure shoots originate at aerial tillers from the axil- 1. The principal the distal side of lary buds of the leaves, and shoot is surround- the first one (posi- simultaneously started to ed by a sheath of tive angle, sensu differentiate a rhizome that several layers of Routledge, 1987), determined the plant’s radial sclerenchyma cells. although in some centrifugal growth. Lateral stems are of the cases there The rhizomes had very protected by the was a reversion short internodes and sym- sheath blade. A forming a negative podial ramification, because rhizome, which angle in relation to the apex differentiated an would be evident the previous ones. orthotropic shoot and a sub- as a longitudinal A 6.5 month-old apical bud that continued stem structure, is plant had eight pri- plagiothropic growth. All not seen. mary shoots, two of rhizome nodes differenti- The rhizome them forming an- ated shoots, which could was observed in a gles which reverse differentiate one or several 35.1cm high plant the circumference “daughter” tillers from the with six emerged Figure 3. Diagram of the angles between the first and sub- (shoots 5 and 7; basal nodes, resulting in a shoots, six months sequent shoots. A: 6.5 month-old plant with 8 shoots, b: 7 Figure 3a). In the very tight and compact tus- after germination month-old plant with 10 shoots. Arrows show growth direc- 7 month-old plant sock. The rhizomes grew in (Figure 2). A stem tion. the position of 10 a centrifugal way; however, structure in the primary shoots can sometimes they branched, longitudinal section is ob- that have sclerenchyma be observed and, accord- i.e. the bud did not produce served at the base of the cells. There are also several ing to the thickness of the an aerial shoot but originated plant, as well as stems in layers of sclerenchyma and bases of the shoots, it was rhizomes of higher order the transversal section, roots parenchyma cells with thick- evident that rhizomes dif- that continued to grow. A and an emerging bud pro- ened walls in the blades of ferentiated in some of them branching pattern, such as tected by the blades sheath sheaths that protect the apex and they were very near to a number of nodes between

JUN 2007, VOL. 32 Nº 6 401 two successive also starch grains Discussion ramifications, was at the base of the not observed, and sheath that emerg- The growth pattern of the usually the angle es from rhizomes, whole tussock of S. argen- between a rhi- more densely at the tinensis, which allows it to zome and another abaxial side. occupy space in all its rays of higher order simultaneously without leav- was ~30º. Initial Structure analysis ing gaps and preventing the growth stages are of adult plants and establishment of other spe- slow, and only af- their response to cies, resembles what Lovett- ter six months the Figure 5. Cross section of a rhizome of S. argentinensis. Scle- disturbance Doust (1981) and Schmid tussock is formed renchyma and parenchyma tissues are visible. A bud is emerging and Harper (1985) termed with an aerial protected by lignified tissue. The central area “phalanx” growth (centrifu- shoot system, with of the three plant gal and multidirectional). shoots concentrated size g roups was As a result of this centrif- at the base and a observed dead and ugal and multidirectional system of half-bur- undergoing dif- growth, S. argentinensis ied rhizomes. The ferent deg rees of plant structure is compact inflorescences dif- decomposition. In and formed by a high num- ferentiated around t he la rger pla nts ber of aerial shoots with midsummer (Janu- the ratio between internodes that have not ary), in two-year t he cent ra l a rea elongated, and therefore old plants and, a nd t he t ussock their meristems are pro- as in other grass- diameters was ap- tected by the sheaths of all es, all internodes proximately three the emerged leaves, which elongated during times la rger t ha n have layers of sclerenchy- this pre-flowering in two sma l ler ma cells. This growth pat- period. The inflo- g roups of pla nts, tern results in an adaptive rescence emerged which means that feature in face of the most wrapped in the flag as plants aged, the common disturbance factor, leaf of the shoot. Figure 6. Cross section of a rhizome and longitudinal section central area, al- which is fire, and together After f lowering, of an emerging shoot bud of S. argentinensis, protected by ready senescent, with its high photosynthet- the shoot aged and the sheath bases. increased faster ic rate even under drought died. than the plant di- conditions (Feldman et al., with the vascular bundles ameter (Table I). In the 2004) are characteristics Rhizome anatomy surrounded by a sheath of three kinds of plants used, that enable S. argentinensis thick layers of sclerenchyma the first and sometimes the to form almost monospe- Rhizomes had lignified cells. Emerging buds are first and second nearest cific stands (Feldman and tissues of several cell lay- protected by the sheath bas- shoot to the central senes- Lewis, 2005). ers, cells thick sclerenchy- es that wrap rhizomes and cent part of the plant and Sarmiento (1992) pointed ma strip, all with thick- shoots, which have highly still bearing at least one out that in grasses where ened and lignified walls lignified subepidermic tis- green leaf, were not dyed there is no elongation of (Figure 5). The vascular sue layers (Figure 6). The with tetrazolium, indicat- vegetative shoots, such as bundles are arranged in the iodine-iodite dye indicated ing that they did not have Leptocoryphium lanatum, characteristic atactostelae that rhizomes had a high living meristematic tissue. Sporobolus cubensis and of grasses, surrounded by density of round and simple All other buds were meta- Elyonurus adustus, mer- lignified tissue. A central starch grains that occupy bolically active. istems are buried in the cavity that occupies part of most of the parenchyma When incubated in humid soil, thus ensuring re-sprout the pith is evident together cells volume. There were sand, central shoots did not after defoliation. In the restart growth after they case of S. argentinensis, the were cut. Only those shoots meristems of the rhizomes Table I that were in the outer circle are half-buried in the soil Diameters of Spartina argentinensis tussocks restarted growth, forming and the aerial shoots are (cm) corresponding to three groups of plants the quasi circular monk’s protected by strongly lig- of increasing diameters * tonsure-like gaps (MTLG). nified cataphyll-like leaf In plants with diameters sheaths. Starch grains in Group MD SCA SCA /MD (*) >25cm (classes II and III), the rhizome as well as in the periphery circle did not the sheath would provide I 10.34 ±0.59 1.24 ±0.17 0.121 a always restart growth ho- a source of energy to al- II 27.60 ±1.15 5.78 ±0.52 0.149 ab mogeneously and in several low tiller regeneration after cases it was evident that fire until the plant shoot III 43.27 ±1.62 16.2 ±1.12 0.377 c 2-4 groups of shoots were is again photosynthetically * I: 7-15cm, II: 25-30cm, III: 40-45cm (n=10, 6 and 3, respectively). Aver- not parts of the same tus- independent. age ±SEM. sock any more, but they The results show that the MD: maximum diameter, SCA: senescent central areas. Values followed by had formed new individuals basic structure of the tus- the same letter are not statistically different, p<0.05). instead. sock is already developed

402 JUN 2007, VOL. 32 Nº 6 before the plant is one year the figures of the final grass, Spartina argentinensis aptativos das partes veg- old. Only in the summer draft, the Federico Wilder- Parodi. Flora 199: 491-499. etativas de Spartina densi- f lora Brong. (Gram ineae) of the second year some muth Foundation for per- Feldman SR, Lewis JP (2005) Ef- da marisma do estuário da shoots will flower and pro- mission to work with plants fect of fire on the structure lagoa dos Patos-RS. Acta duce seeds, ageing later, from their Reserve, and the and diversity of a Spartina Bot. Bras. 5: 3-16. while the rhizomes contin- Consejo Nacional de Inves- argentinensis tall grassland. ue growing and new tillers tigaciones Científicas y Tec- Appl. Veget. Sci. 8: 77-84. Perreta MG, Vegetti AC (2005) Patrones estructurales en emerge from the bases of nológicas (CONICET) for Godin C (2000) Representing las plantas vasculares: una the already grown shoots. financial aid. and encoding plant architec- revisión. Gayana Botanica. Parallel to the tussock ture. A review. Ann. Forest 62: 9-19 growth, dead organic mat- REFERENCES Sci. 57: 413-438. ter accumulation starts as Routledge RD (1987) Rhizome Adachi N, Ichiro T, Takahashi Godin C, Costes E, Sinoquet architecture for dispersal in a result of i) shoots which H (1999) A method for de- Eleocharis palustris. Can. J. have flowered, ii) shoots M (1996) Central die-back of monoclonal stands of scribing plant architecture Bot. 65: 1218-1223. which die before flowering, Reynoutria japonica in an which integrates topology and iii) senescence of basal early stage of primary suc- and geometry. Ann. Bot. 84: Ruiz Leal A (1959) El desar- leaves of shoots that are cession on Mount Fuji. Ann. 343-357. rollo de estructuras subcir- Bot. 77: 477-486. culares en algunas plantas. still alive. This accumula- Harper JL (1977) Population Rev. Agron. Nordeste Arg. tion of dead matter will Anderson CE (1974) A review Biology of Plants. Aca- 3: 83-138. favor initiation and propa- of structure in several North demic Press. London, UK. gation of fire. Carolina salt marsh plants. In 892 pp. Ruzin S (1999) Plant Micro - Rendd RJ, Queen WH (Eds.) technique and Microscopy. No regrowth was resumed Hickey M, Clive K (2000) Illus- in any of the disturbed Ecology of halophytes. Aca- Oxford University Press. demic Press. London, UK. trated Glossary of Botani- Oxford, UK. 534 pp. plants of their geometrical 605 pp. cal Terms. Cambridge Uni- center, not as consequence versity Press. Cambridge, Sampaio MC, Araújo TF, Scar- of cutting or burning but Busso CA, Boo RM, Pelaez DV UK. 208 pp. ano FR, Stefer JF (2004) due to the fact that there (1993) Fire effects on bud Directional growth of a viability and growth of Stipa Knapp AK (1985) Effect of fire clonal bromeliad species in was no living tissue before tenuis in semiarid Argentina. and drought on the eco - response to spatial habitat the disturbance, though the Ann. Bot. 71: 377-381. physiology of Andropogon heterogeneity. Evol. Ecol. gaps were not evident be- gerardii and Panicum vir- 18: 409-428. Cabrera AL, Willink A (1973) gatum in a tallgrass prairie. cause long leaves completely Ecology 66: 1309-1320. covered it. The data indi- Biogeografía de América Sarmiento G (1992) Adapta- Latina. Serie de Biología, cate that in S. argentinensis, tive strategies of perennial Monografía Nº 13. OEA. Levering CA, Thomson WW grasses in South American “hollow crowns” (Strick- Washington, USA. (1972) Studies of the ultra- savannas. J. Veget. Sci. 3: land, 1983) or “monk’s ton- structure and mechanism of 325-336. sure-like gaps” (Lewis et Caldwell PA (1957) The spa- secretion of the salt gland tial development of Spartina of the grass Spartina. Proc. al., 2001) are the result of 3 0 th Electron Microscope Schmid B, Harper JL (1985) colonies growing without Clonal growth in grassland the ontogeny and senescence competition. Ann. Bot. 21: Soc. of America. pp. 222- 223. perennials. I. Density and of the tussock, as it was al- 203-216. pattern-dependent compe- ready suggested for Festuca tition between plants with Carlquist S (1982) The use of Lewis JP, Stofella SL, Prado ovina. Working with plants DE, Pire EF, Franceschi different growth forms. J. ethylendiamine in soften- Ecol. 73: 793-808. obtained from seeds and ing hard plant structures for EA, Carnevale NJ (1990) adult plants not subjected paraffin sectioning. Stain Dynamics and development Strickland R (1983) Hollow to grazing or fire, it was Technol. 57: 311-317. of floristic richness in the vegetation of a large de - crowns: overgrazing, under- shown that in S. argenti- grazing, or old age?. Range- Danin A, Orshan G (1995) Cir- pressed area of the Great lands 5: 13-14. nensis tussocks the forma- cular arrangement of Stipa- Chaco. Flora 184: 63-77. tion of a central gap is a grostis ciliata clumps in the consequence of its tillering Negev, Israel and near Go- Lewis JP, Stofella SL, Feldman Sutherland GK (1916) The physi- ological anatomy of Spar- pattern and rhizome growth, kaeb, Namibia. J. Arid Envir. SR (2001) The origin of 30: 307-313. tonsure like gaps in Spar- tina towsendii. Ann. Bot. which constitute its normal tina argentinensis Parodi. 30: 333-351. architecture. Although the Dizeo de Strittmater C (1979) Rev. Biol. Trop. 49 : 313- phenomenon begins when Modificación de una técnica 316. Uresk DW, Rickard WD, Cline the plant is younger than de coloración safranina-fast JF (1980) Perennial grasses and their response to a wild- a year, it will become evi- green. Bol. Soc. Arg. Bot. Lovett-Doust L (1981) Popu- 18: 121-122. lation dynamics and local fire in south-central Wash- dent only after the second specializations in a clonal ington. J. Range Manag. 33: or third year. Different en- Eskuche U (1992) Los espar- pla nt Ranunculus repens 111-114. vironmental factors such tillares, un monumento II. The dynamics of ramets as grazing and fire, do not histórico pre-colombino en el in contrasting habitats. J. Walsh GE (1990) Anatomy of tapiz vegetal del NE argen- Ecol. 69: 743-755. the seed and seedling of trigger the formation of the tino. Herbarium Humboldtia- Spartina alterniflora Lois. central gap; they only allow num. Universidad. Nacional Metcalfe CR (1960) Anatomy (Poaceae). Aquatic Bot. 38: it to be seen. del Nordeste. Argentina. 37 of the Monocotyledons. 177-193. pp. Vol I. Gramineae. Claren- ACKNOWLEDGEMENTS don Press. Oxford, UK. Wikberg S, Mucina L (2002) Feldman SR, Bisaro V, Lewis JP 731 pp. Spatial variation in vegeta- (2004) Photosynthetic and tion and abiotic factors rela- We authors thank JM growth responses to fire of Perazzolo M, Pinheiro F (1991) tive to a ring-forming sedge. Vázquez for his help with the subtropical-temperate Aspectos anatómicos e ad- J. Veget. Sci. 3: 677-684.

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