Fungi and Bacteria Associated with Leaves During Processing in a Woodland Stream

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Autumn—shed leaves of white oak (Quercus alba) and pignut hickory (Carya glabra) were fastened together and incubated in a third order hardwater stream in south—western Michigan. At biweekly intervals, leaves were removed and the microbial populations assessed. Direct counts of bacteria increased logarithmically with time, but viable counts were generally lower. Flexibacter, Achromobacter, Flavobacteria, Pseudomonas, and Cytophaga were isolated from leaves. No apparent bacterial succession was detected. The mycoflora was assessed in five ways, including direct examination and incubations ranging from environment simulating to particle platings on nutrient medium. Although this last technique suggested that common soil and litter fungi dominated, direct examination and environment—simulating incubations showed that aquatic hyphomycetes, particularly Alatospora acuminata, Flagellospora curvula, and Tetracladium marchalianum were the dominant members of the mycoflora. The successional pattern of these fungi on both leaf species is discussed. It is concluded that the aquatic hyphomycetes are actively growing and completing their life cycle in this environment and that the terrestrial fungi are normally present mainly in a dormant state, growing and sporulating only in greatly enriched conditions. The highest ATP levels observed corresponded to the periods of highest fungal frequencies .