Plant detritus breakdown in the hyporheic zone of headwater streams: importance of fungal decomposers

In headwater streams, leaf litter decomposition constitutes a key ecosystem-level process. The objective of this thesis was to characterize leaf decomposition in the hyporheic habitat of streams, quantify the associated dynamics of fungal and invertebrate decomposers together with the effect of abiotic factors, and incorporate this process into a stream ecosystem perspective. Taken as a whole, these findings suggest that the functioning of woodland stream ecosystems, largely based on trophic relationships and carbon dynamics related to leaf decomposition occurring at the sediment surface, should be reconsidered with the incorporation of the vertical dimension conceptualized by "hyporheologists". These results lead to think out the dynamics and role of aquatic hyphomycetes at a broader scale than the stream water column alone, and highlight the crucial function of the hyporheic zone, which up to now remained mostly neglected to this regard.