400 S.-Afr.TydskT.Plantk., 1992, 58(5)

Specimens examined The distribution of C3 and C4 plants in a Calonectria hederae, Hedera helix leaf, Great Britain, 1958, successional sequence in the Okavango IMI 75300 (holotype); C. hederae. Hedera helix leaf, Great Delta Britain, 1978, IMI 241261; C. hederae. Hedera helix leaves, France, 1948, G. Arnaud, IMI 39232 (lectotype); Cylindro­ carpon reteaudii, on Smithia bequaertii, Indo China, F. Karen Ellery,* W.N. Ellery* and 8.Th. Verhagent Bugnicourt, 1M! 55922 (dried culture derived from type, 'Department of Botany, University of the Witwatersrand. P.O. Herb Paris). Wits, 2050 Republic of South Africa tSchonland Research Centre, University of the Witwaters­ Culture examined rand, P.O. Wits, 2050 Republic of South Africa C. leucothoeae, from Leucothoeae axillaris leaves, Florida, Received 8 January 1992; revised 26 May 1992 U.S.A., Feb. 1988, EI-Gholl, ATCC 64824 (type culture). Carbon isotope techniques were used to determine the Acknowledgements photosynthetic pathway of a number of wetland plant The authors thank the International Mycological Institute, species. The relative cover abundances of C3 and C4 plants Kew, Surrey (lMI), and the American Type Culture Collec­ were compared along a successional sequence of the tion, Rockville, Maryland (A TCC), for placing specimens Maunachira River system of the Okavango Delta. Plants with and cultures at our disposal. a C3 photosynthetic pathway were dominant in early succes­ sional stages and C4 plants were dominant in late References successional stages. It is proposed that nutrient availability, particularly nitrogen limitation, could be a determinant of the ARNAUD. G. 1952. Mycologie Concrete: Genera. Bull. Soc. change from C3 to C4 plant dominance during succession. Mycol. Fr. 68: 181 - 223. BOESEWINKEL. H.I. 1982. Heterogeneity within Cylindrocla­ Die fotosintetiese verloop in 'n aantal moerasplante is deur dium and its teleomorphs. Trans. Br. mycol. Soc. 78: 553 - middel van koolstof-isotooptegnieke vasgestel. Die relatiewe 556. dekkingsdigthede van C3 en C4 plante in opeenvolgende BOOTH, C. 1966. The genus Cylindrocarpon. Mycol. Pap. 104: seksies van die Maunachira riviersisteem van die Okavango 1 - 56. Delta is met mekaar vergelyk. In die aanvanklike seksies was BOOTH. C. & MURRAY, 1.S. 1960. Calonectria hederae plante met 'n C3 fotosintetiese verloop dominant. terwyl C4 Arnaud. and its Cylindrocladium conidial state. Trans. Br. plante in die daaropvolgende seksies dominant was. Daar mycol. Soc. 43: 69 - 72. word voorgestel dat die beskikbaarheid van voedingstowwe, BUGNICOURT, F. 1939. Les Fusarium et Cylindrocarpon de veral stikstof, 'n rol speel in die verandering van C3 l'Indochine. Encycl. Mycol. 11: 1 - 206. dominansie na C4 dominansie. CROUS. P.W., PHILLIPS, AJ.L. & WINGFIELD. M.l. 1991. The genera Cylindrocladium and CylindrocladieUa in South Keywords: carbon isotope, C3• C4• nutrients, Okavango Africa, with special reference to forest nurseries. S. Afr. For. J. Delta, succession. 157: 69 - 85. EL-GHOLL. N.E., LEAHY, R.M. & SCHUBERT, T.S. 1989. Cylindrocladium leucothoeae sp. nov. Can. J. Bot. 67: 2529 - The C4 photosynthetic pathway has been shown to have an 2532. adaptive advantage under conditions of high temperature, FISHER, N.L.. BURGESS, L.W., TOUSSOUN, T.A. & high irradiance and in an arid environment (Osmond et al. NELSON, P.E. 1982. Carnation leaves as a substrate and for 1982; Pearcy & Ehleringer 1984). The field studies in which preserving cultures of Fusarium species. Phytopathology 72: the distribution of C3 and C4 plant species was investigated, 151 - 153. have been either along environmental gradients (Tieszen et PEERALLY, A. 1974. CMI Descriptions of Pathogenic Fungi and al. 1979; Boutton et al. 1980) or on a phyto-geographical Bacteria No. 426. basis (Vogel et al. 1978; Ellis et al. 1980; Cowling 1983; PEERALLY, A. 1991. The classification and phytopathology of Hattersley 1983; Vogel et al. 1986). No work relating Cylindrocladium species. Mycotaxon 40: 323 - 366. SHERBAKOFF, C.D. 1828. Washington palm leaf spot due to photosynthetic metabolic pathways to a successional sequence of plant communities has been conducted. Cylindrocladium macrosporum n. sp. Phytopathology 18: 219 - 225. The area of the present study was the permanently SOBERS, E.K. 1967. Morphology and pathogenicity of Cylindro­ inundated Maunachira River system situated in the north­ cladium macrosporum and C. pteridis. Phytopathology 57: eastern part of the Okavango Delta, north-western 464. Botswana. The vegetation consists of a heterogeneous mix SOBERS, E.K. 1968. Morphology and host range of Cylindro­ of wetland plant communities comprising submerged and cladium pteridis. Phytopathology 58: 1265 - 1270. floating-leaved species dominant in deep open water bodies SOBERS, E.K. & ALFIERI, S.A. 1971. Species of Cylindro­ and short, emergent plant species dominant in shallow peat cladium and their hosts in Florida and Georgia. Proc. Fla. bogs. A successional sequence for the wetland plant State Hortic. Soc. 85: 366 - 369. communities of the study area, based on phytosociological WOLF, F.A. 1926. Brown leaf spot of leather fern. 1. Elisha associations and peat stratigraphy, is described by Ellery et Mitchell Sci. Soc. 42: 55 - 62. al. (1991). S.AfrJ.Bot., 1992, 58(5) 401

Carbon isotope analysis was used as an indicator of Submerged plant assemblages rooted in deep water sites photosynthetic pathway type. Species chosen for analysis (stage A) are exposed to low levels of irradiance. The plant were important components in one or more of the succes­ communities in later successional stages (stages B - F) have sional stages and comprised mainly grasses and sedges relatively open canopies where very little shading occurs. It which dominate the landscape. Gas samples for carbon isotope analysis were produced using a modified Dumas combustion method (Macko & Parker 1983). Approximately Table 1 Photosynthetic pathways (PP) and l)13C (%0 PDB) values of a number of plant species in the Maunachira 5 mg of dry, powdered plant material was added to silica River system ampoules containing CuO, Cu and Ag previously degassed at 400°C. Ampoules were evacuated, lightly flamed, sealed and heated to 900°C. After slow cooling, seals were broken Plant species at liquid-nitrogen temperature and ampoules were again Cyperus peetinatus Yahl ~ -26.0 evacuated. CO2 gas was then released at -80°C into the inlet Eleocharis acutangula (Roxb.) Schult.b C3 of a Micromass 602C mass spectrometer. The carbon iso­ Eleocharis dulcis (Bunn.F.) Hensch. ~ -26.0 tope ratios were measured in duplicate and expressed as Ficus verruculosa Warb" C3 -26.8 813C values in permille (%0) with respect to PDB Standard§. Fuirena puhescens (poir.) Kunthb C3

Measurement precision is estimated at +0.10/00. Whilst F uirena stricta Steud. C3 -27.1 known C3 plants have 813C values around -270/00, known C4 Fuirena umbel/ata Rottb. b ~ plants have 813C values around -120/00. CAM plants have Ludwigia leptocarpa (Nutt.) Hara' C3 -26.1 mainly intermediate values (Deines 1980). Panicum parvifolium Lam. b ~ b Mean percentage cover of each of the C3 and C4 plant Phragmites australis (Cav.) Steud. C3 b species within each successional stage was determined and Sacciolepis africana C.E. Hubb. & Snowden C3 the overall contribution of each of these types to total cover Scirpus cubensis Poeppig & Kunth ex Kunthlt C3 Scleria woodii C.B.CLb C3 was estimated. Thelypteris confluens (lbunb.) Morton' C -28.2 The results of the carbon isotope analysis, as well as the 3 Typha capensis (Rohrb.) N.E.Br. ~ -28.1 photosynthetic pathway of major plant components in the Cyperus articulatus L. b C4 study area, are presented in Table 1. The analysis of Eriochrysis pal/ida Munro C4 -12.6 percentage cover of each of the C3 and C4 plant species in Imperata cylindrica (L.) Raeuschel C4 -12.8 each successional stage shows that C3 plant species are Miscanthus capensis Nees Anderss. var capensis C4 -12.3 present with a higher abundance than C4 species in the first Panicum repens L. b C4 three successional stages (Figure 1), namely A, Band C, Pycreus mundtii Neesb C4

which comprise deep-water communities dominated by sub­ Pycreus nitidus (Lam.) J. Raynal C4 -11.9 merged, floating-leaved and tall emergent plant species. The Vossia cuspidata (Roxb.) Griff.b C4 opposite was apparent in the last three successional stages Nymphaea caerulea Sav.' CAM -22.3 (D, E and F). The greatly increased relative cover of C4 , Omitted from succession analysis species in these three stages was due to the dominance of b Photosynthetic pathway determined from other studies the C4 sedge Pycreus nitidus in the floating sudd communities of Stage D and the presence of many short emergent C4 species such as Eriochrysis pallida, Vossia 100 cuspidata, lmperata cylindrica and Miscanthus capensis var. capensis in the shallow peat bog communities of stages E 90 ~ 80 and F (Ellery et al. 1991). Non-sedge and non-grass species o u present in each successional stage were not included in the OJ 70 OJ analysis, as their relatively minor contribution to total cover C'" eo would have had little effect on the observed distribution OJ ~ 50 0.. pattern of C3 and C4 plants. 2 «) The time span of the successional sequence from deep '" (4 m) water bodies colonized by submerged, floating-leaved .~en 30 and tall emergent plant species (stages A, B & C, Figure 1) W 20 to floating sudd communities (stage D), to peat bog com­ 10 munities of less than half a metre water depth dominated by o A B c o E F short, emergent wetland species (stages E & F) has been Successional stage estimated to be in the order of one to two centuries in the study area (p. Smith, Dept. of Water Affairs, Maun, Figure 1 The relative proportions of cover abundance of C3 and Botswana, pers. commun.). Throughout this time, peat has C4 grasses and sedges in each of the six recognized successional stages A - F (early - late succession). The pertinent features of gradually accumulated, indicating that permanently inun­ each stage are as follows: A, submerged species, deep water; dated conditions have prevailed and lack of water has thus B, floating-leaved and tall emergent species, deep water; C, float­ not been limiting to plant growth. ing-leaved and tall emergent species with organic sudds, deep water; D, floating sudd dominated by Pycreus nitidus; E, short § l)13C = (1 - Rumple / RPOB ) X 1000% where R = (13C) / e2C) emergent species rooted in peat, heterogeneous; F, short emergent PDB (PeeDee Belemnite) is the international marine limestone species rooted in peat, homogeneous, often dominated by Miscan­ standard. thus capensis var. capensis. 402 S.-Afr.Tydskr.Plantk., 1992,58(5)

is suggested that the light environment for plants is rela­ BROWN, R.H. 1978. A difference in N use efficiency in C3 and tively similar in these successional stages and does not C4 plants and its implications in adaptation and evolution. appear to be a determinant of photosynthetic type. The only Crop Sci. 18: 93 - 98. BROWN, R.H. 1985. Growth of C3 and C4 grasses under low N exception is in situations where the C4 species Miscanthus capensis var. capensis occurs. It forms a dense canopy levels. Crop Sci. 25: 954 - 959. CHRISTIE, E.K. & DETLING, J.K. 1982. Analysis of inteference restricting light to other species. Measures of levels of between C and C grasses in relation to temperature and soil irradiance in each of the communities would corroborate or 3 4 nitrogen supply. Ecology 63: 1277 - 1284. refute this. COWLING, R.M. 1983. The occurrence of C3 and C4 grasses in Water nutrient status was measured (Ellery et al. 1991) fynbos and allied shrublands in the South Eastern Cape, South but showed no relationship to community distribution, with Africa. Oecologia 58: 121 - 127. all levels of nitrogen and phosphorus being extremely low DEINES, P. 1980. The isotopic composition of reduced organic and frequently beyond limits of conventional detection. Peat carbon. In: Handbook of environmental isotope geochemistry, nutrient levels have not been recorded in the study area. eds. P. Fritz & J.Ch. Fontes, pp. 329 - 406. Elsevier, However, nutrients may become increasingly limiting for Amsterdam. plants during the successional sequence (Ellery 1987), as ELLERY, K. 1987. Wetland plant community composition and peat deposits trap nutrients rendering them unavailable for successional processes in the Maunachira river system of the Okavango Delta. MSc thesis, University of Witwatersrand, plant uptake (Moore & Bellamy 1974). Wilson and Haydock Johannesburg. (1971), Brown (1978, 1985) and Schmitt and Edwards ELLERY, K., ELLERY, W.N., ROOERS, K.H. & WALKER, (1981) noted that C plant species utilize nitrogen more effi­ 4 B.H. 1991. Water depth and biotic insulation: major ciently than C3 species, and suggested that they were better determinants of back-swamp plant community composition. adapted to nutrient-, particularly nitrogen-deficient situa­ Wetlands Ecol. Manag. 1: 149 - 162. tions. Christie and Detling (1982) examined the relationship ELLIS, R.P., YOOEL, J.e. & FULS, A. 1980. Photosynthetic of nitrogen use efficiency (NUE) under conditions of differ­ pathways and the geographical distribution of grasses in South ent temperatures. They found that the NUE of C4 plants was West Africa, Namibia. S. Afr. 1. Sci. 76: 307 - 314. higher under conditions of high temperature (30/15°C for HATTERS LEY, P.W. 1983. The distribution of C3 and C4 grasses day/night) but that that of C3 plants was higher under condi­ in Australia in relation to climate. Oecologia 57: 113 - 128. tions of lower temperatures (20/12°C). The mean day/night MACKO, S.A. & PARKER, P.L. 1983. Stable nitrogen and air temperatures in the study area are 32/17°C in summer carbon isotope ratios of beach tars on South Texas barrier and 27/14°C in winter. The high habitat temperatures and islands. Marine Env. Res. 10: 93 - 103. MOORE, P.D. & BELLAMY, D.I. 1974. Peatlands, 220 pp. Paul the gradient of decreasing nitrogen availability from early to late successional stages may be factors determining the Ele\c, London. OSMOND, C.B., WINTER, K. & ZIEGLER, H. 1982. Functional observed distribution pattern of C3 and C4 plants in the significance of different pathways of C~ fixation in photo­ study area. No significant gradient of water temperature was synthesis. Encyclopaedia of plant physiology, Yol 12B, pp. found in the study area (Ellery 1987). 480 - 547. Springer Yerlag, Berlin. Many characteristics of the plant species themselves, such PEARCY, R.W. & EHLERINGER, J. 1984. Comparative eco­ as life form, life history as well as physiological attributes, physiology of C3 and C4 plants. Pl. Cell Environ. 7: 1 - 13. all contribute to their distribution patterns. The reasons for SCHMITT, M.R. & EDWARDS, G.E. 1981. Photosynthetic the trend in change in distribution of plant species in the capacity and nitrogen use efficiency of maize, wheat and rice: study area over time is thus likely to be more complex than A comparison of C3 and C4 photosynthesis. 1. Exp. Bot. 32: has been presented here, but the availability of nitrogen 459 - 466. could account for some of the observed patterns and should TIESZEN, L.L., SENYIMBA, M.M., IMBAMBA, S.K. & be investigated further. TROUGHTON, J.H. 1979. The distribution of C3 and C4 grasses and carbon isotope discrimination along an altitudinal Acknowledgements and moisture gradient in Kenya. Oecologia 37: 337 - 350. YOOEL, J.C, FULS, A., & ELLIS, R.P. 1978. The geographic Profs. T.S. McCarthy and K.H. Rogers and a referee are distribution of Kranz grasses in South Africa. S. Afr. 1. Sci. 74: thanked for comments on the manuscript. The University of 209 - 215. the Witwatersrand provided funding for the study. YOOEL, J.e., FULS, A. & DANIN, A. 1986. Geographical and environmental distribution of C3 and C4 grasses in the Sinai, References Negev, and Judean deserts. Oecologia 70: 258 - 265. BOUTTON, T.W., HARRISON, A.T. & SMITH, B.N. 1980. Dis­ WILSON, J.P. & HAYDOCK, K.P. 1971. The comparative re­ tribution of biomass of species differing in photosynthetic sponse of tropical and temperate grasses to varying levels of pathway along an altitudinal transect in a southeastern nitrogen and phosphorus nutrition. Aust. 1. Agric. Res. 22: Wyoming grassland. Oecologia 45: 287 - 298. 573 - 587.