Inter- and intraspecific functional variability of aquatic fungal decomposers and freshwater ecosystem processes

Although considerable intraspecific trait variation is common, research dedicated to ecosystem functioning has focused mainly on species diversity. Organic matter breakdown, a key ecosystem-level process in woodland streams is mainly driven by aquatic hyphomycetes. These aquatic fungal decomposers constitute a critical link between plant litter and invertebrate detritivores in detritus-based food webs in streams. In this study, we evaluated the functional variability across a set of ten isolates each belonging to five widespread aquatic hyphomycete species, namely Articulospora tetracladia, Anguillospora crassa, Lemonniera terrestris, Neonectria lugdunensis and Tetracladium marchalianum. All the isolates originated from undisturbed streams. We estimated inter- and intraspecific variability on growth rates, litter decomposition and sporulation rates of the isolates. In addition, we also assessed the invertebrate consumption rates on leaves colonized by different isolates. Significant differences were observed within the fungal species in growth rates (A. crassa, L. terrestris, N. lugdunensis and T. marchalianum), leaf litter decomposition (A. tetracladia, L. terrestris and N. lugdunensis) and sporulation rates (A. crassa, A. tetracladia, L. terrestris and N. lugdunensis). The relative consumption rates of the shredder Schizopelex festiva significantly differed when fed with leaves colonized by isolates of L. terrestris and N. lugdunensis, however differences were not seen when fed with leaves conditioned by different species. Overall, results indicate substantial intraspecific functional variability among the isolates of aquatic hyphomycetes. Besides, our study also provides a novel insight that intraspecific functional variability is a natural phenomenon exhibited by isolates not only from polluted but also from undisturbed streams. Here the isolates demonstrated marked inter- and intraspecific functional variability, calling for a greater understanding of the functional role of aquatic hyphomycetes and its ability to influence higher trophic levels.