‘Contribution of aquatic Hyphomycete communities to leaf decomposition and food webs in alpine streams’

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Department of Environmental Management and Ecology, School of Life Sciences, Faculty of Science, Technology and Engineering, La Trobe University, Bundoora.

Fungi are important decomposers of organic matter in both terrestrial and aquatic environments. In streams, aquatic Hyphomycetes are the fungal group responsible for leaf litter decomposition. Knowledge regarding this group is predominantly Northern Hemisphere dominated. Alpine studies are underrepresented in the literature, especially in Australia, with only one previous study. This thesis provides new information about the ecology of the fungal community present within Australian alpine streams. Specifically, I outline seasonal influences on the fungal community and how this affects the decomposition of Eucalyptus pauciflora both physically and chemically, and the role of fungal conditioning of these leaves in the food web of alpine streams. Measures of stream physico-chemical properties revealed seasonal variation driven predominantly by climate and the influence of biological and chemical processes occurring within upstream peatlands. Physical and chemical alterations to E. pauciflora leaves were determined via leaf mass loss, along with Synchrotron based infrared analysis. Fungal material was found to concentrate around the xylem tissues where active fungal decomposition was evident in the breakdown of lignin and carbohydrate. Fungal community changes were assessed via seasonal estimates of biomass and reproductive output, along with 454-pyrosequencing. Reproductive activity was greatest in the warmer seasons, with a seemingly dormant state occurring during the winter. The most noticeable community changes were revealed by DNA analysis as the pre-existing terrestrial fungal community was ultimately replaced by aquatic fungal species. The importance of conditioned leaves to alpine stream food webs was investigated using stable isotope analysis and 454-pyrosequencing. Despite being a common component in stream detritus, conditioned leaves were not found to be a dominant resource during summer. Alpine stream food webs appear complex, driven by autocthonous resources and terrestrial fall- ins which are utilised by the top-predator, Galaxias olidus. This thesis has added to Australia-specific knowledge, which is important for predicting impacts and guiding management decisions in an environment sensitive to climatic changes. It also highlighted the benefits of cross disciplinary approaches, along with combining traditional and novel techniques to study fungal community dynamics. Knowledge gaps were highlighted, particularly in genetic databases and genetic data analysis.