The problem being investigated: Our aim was to understand a uninvestigated process on energy and nutrient flow in headwater streams: the fate of fungal spores. Headwater streams rely on allochthonous organic matter (mainly leaf litter and woody debris), which is used as energy source by aquatic hyphomycete decomposers. Fungal biomass may account for up to 8% of leaf litter mass in streams, and about 50% of their assimilated carbon (C) is converted into reproductive spores. The spores are a major component of fine particulate organic matter (FPOM), an important fraction of (C) fluxes in detritus-based systems. Yet, their role on headwater stream food webs has been overlooked, although they could be a non-negligible source of nutrients and essential molecules for aquatic filter feeder and collector consumers.
Why is it important for the society: This project brings new information on the relation between an anthropogenic constraint (nutrient loads) and the integrity (biotic and functional) of an essential component responsible of the mineralization of huge quantities of terrestrial carbon. Understanding how our activities are affecting natural nutrient cycles, and the responsible of these cycles contribute towards European policy objectives (biodiversity) and strategies (conservation).
Overall objectives:
1. Investigate the chemical factors controlling aquatic hyphomycetes' sporulation and deduce if global changes could modulate the sporulation process and the intrinsic quality of spores.
2. Study the role of aquatic hyphomycete spores as a resource for consumers in headwater streams by characterizing their elemental (C, N and P) and biochemical (FA and sterols) composition.
Conclusions of the action (achievements):
(1) Production of fungal mycelia without exposing it directly to the medium. (2) Demonstration that fungal mycelia produce spores differing in size when exposed to different nutrient ratios. This new finding has important implications in a global warming context where natural nutrient ratios are affected by anthropogenic activities. (3) Demonstration that certain stoichiometric ratios affect spores of mycelia exposed to different nutrient ratios. (4) Demonstration that the chemical complexity of essential nutrients (C, N and P) needs to be considered when studying the effect on biological traits. We showed that phosphorus chemical complexity can increase fungal spores biovolume, and the essential ratios CN and CP. This can have consequences in their potential trophic quality.
