Processing of Eucalyptus viminalis leaves in Australian streams - importance of aquatic hyphomycetes and zoosporic fungi

The decomposition of Eucalyptus viminalis leaves was examined over 8 weeks in 3 streams, each with two sites, in New South Wales, Australia. Invertebrate colonization of litter bags was negligible. Recovered leaves were aerated to induce sporulation by aquatic hyphomycetes. Conidial numbers generally started to increase after 28 days of stream exposure. Aerated leaves also released round structures tentatively identified as zoosporic propagules. Maxima were reached after 7 days of stream exposure. High levels of ergosterol were found in leaves after 7 days of stream exposure. Exponential decay rates varied between 0.0030 and 0.0065 (day(-1)) and 0.00018 and 0.00054 (degree day(-1)). Mass loss rates correlated significantly with maximum conidium release, but not with maximum ergosterol levels or maximum zoospore release, measured physicochemical stream parameters, or the presence of riparian vegetation. As reported from Europe and North-America, aquatic hyphomycetes appeared to play a major role in decomposition, but zoosporic fungi, generally ignored, may be involved in early stages of decay.