Species diversity of freshwater hyphomycetes in some streams of Pakistan .2. Seasonal differences of fungal communities on leaves

Significantly more fungal species colonized leaves in summer, spring and autumn during the first week of submersion than in winter. Higher amounts of dry leaf mass were lost in summer, spring and autumn than in winter. Rapid loss of dry mass was accompanied by rapid development of a fungal community. Colonization and sporulation rates varied with each fungal species. Maximum frequency of occurrence of fungal species were reached earlier (3-4 weeks) in summer and spring communities than in communities of autumn (4 weeks) and winter (6 weeks). More conidia were produced per milligram plant material in winter and autumn than in summer and spring. Flagellospora curvula dominated the communities in autumn, winter and spring while Lunulospora curvula dominated the summer community. The occurrence of rich fungal communities on leaves in four seasons is due to the availability of deciduous substrata contributed by the riparian vegetation, supplemented with seasonal addition of wheat and rice straw and enrichment of the canal water with phosphates and nitrates washed down from the bordering fields.