B. Papp szerk.: Studia Botanica Hungarica 35. 2004 (Budapest, 2004)

Gönczöl, János; Révay, Ágnes: Aquatic Hyphomycetes in two streams differing in discharge and distribution of leaf litter

analysed altogether in five tributaries of the Morgó stream system. We concluded that low-order streams had hyphomycete communities with specific features noticeably differing from each other as well as from those in higher-order stream sections of this system (GÖNCZÖL and RÉV A Y 2003). The results of the present and earlier studies showed that the total number of the fungal species in a given tributary was generally similar to that of the stream section where the tributary enters the main stream (GÖNCZÖL et al. 1999). Somewhat more species occurred in the softwater than in the hardwater tributaries, but this pattern was not clear-cut. Higher numbers of species (48-52) occurred at the sites of Deszkametsző, a slightly alkaline tributary (pH 7.5-8.4) than at the sites of Bagolybükk (44-46 species, pH 7.0-8.1). Higher species numbers in the circumneutral than in the hardwater streams have for a long time been recognised and confirmed in many studies (BÄRLOCHER and ROSSET 1981, WOOD-EGGENSCHWILER and BÄRLOCHER 1983, MARVANOVÁ 1984, BÄRLOCHER 1987, CASAS and DESCALS 1997). Some other studies suggest that high diversity of the riparian vegetation is also correlated positively with the species richness of aquatic hyphomycete conidia in transport (FABRE 1996, CASAS and DESCALS 1997, GÖNCZÖL et al. 2003). Whether the unfavourable effect of alkaline stream water to species number may be compensated by the high diversity of substrates is not known presently. We still know little how these confounding effects control the structures of fungal communities in different stream habitats. The amount of leaf and wood litter in the stream sections studied could not be determined either in the present or in earlier studies. To our knowledge there is not an accepted sampling method to reliably estimate the quantity of litter (either leaf or wood or even both) in a given reach of a stream. A survey of the submerged litter in the two tributaries revealed a well recognisable difference in the position and the quantity of leaf litter in the studied reaches of Deszkametsző and Bagolybükk. A continuous, loose layer of leaves covered the streambed at Deszkametsző-1, while a typical patchy distribution of leaves being aggregated in packs was observed at Bagolybükk-1. Due to these differences in the structure of leaf litter we estimated that greater amount of leaf litter per water volume was present in Deszkametsző than in Bagolybükk. We also considered that thick but loose layer of leaves on the streambed at Deszkametsző-1 provides more favourable conditions for fungal sporulation than tightly aggregated leaf packs in Bagolybükk-1. Consequently a higher conidial concentration in stream water in Deszkametsző, at least at site 1, than Bagolybükk-1 was anticipated. The conidial concentrations at the sampling sites differed greatly in the two tributaries. These differences were most pronounced in the November samples.