The application of habitat templets and traits to hyphomycete fungi in a mid-European river system

1. The general knowledge about hyphomycetes is summarized and traits of some of these organisms in the Rhône floodplain are described to assess compliance with the river habitat templet (RHT) and patch dynamics concept (PDC) hypotheses. This investigation corresponds with those for other taxonomic groups reported in a recent Freshwater Biology Special Issue on the Ecology of the Upper Rhône River (Statzner, Resh & Dolédec, 1994). 2. Three groups of fungi were considered: aquatic, terrestrial, and aero-aquatic hyphomycetes. 3. The main factors controlling distribution of these micro-organisms are food (mostly organic matter), dissolved oxygen and biotic interactions. 4. With contrasting strategies, hyphomycetes exploit both fallen leaves, a discrete ephemeral resource, and wood fragments, which are more durable. 5. Fungal propagules (spores, hyphae) are distributed in the water, and even the air, largely throughout the year. This explains the resilience of these organisms to disturbance. 6. A major problem is the spatial (boundary layer, dead zones) and temporal (leaf input) scale at which these micro-organisms live and their interactions at the scale adopted for the other organisms referred to in the Special Issue on the Ecology of the Upper Rhône. 7. Our scant knowledge of the microbial ecology in the Rhône floodplain, together with the scale problem and high microbial resilience to environmental stress, render the RHT and PDC hypotheses difficult to test. Only three traits could be tested on hyphomycetes, but all three confirmed the RHT hypotheses. 8. Hyphomycete communities appear to be biologically controlled in more favourable and temporally stable environments, and physico-chemically controlled in harsher and more perturbed environments.