Combined effects of freshwater salinization and leaf traits on litter decomposition

Freshwater salinization is a matter of major global concern due to its consequences on the aquatic biota and ecosystems functioning. Salt contamination negatively affects the leaf litter decomposition process, a key ecosystem-level process in forested streams that contributes to the recycling of nutrients and carbon storage. However, information on how additional factors may influence the magnitude of the response to salinization is scarce. In this microcosm study we assessed the importance of leaf (Castanea sativa; Quercus robur) traits, on aquatic hyphomycetes-mediated leaf litter decomposition and associated variables, in salt-contaminated (0, 1, 3 and 6 g/l NaCl) environments. The leaves were incubated individually, and in a mixture, for 28 days, under each tested salt concentration. Salinity depressed leaf mass loss, fungal biomass, respiration and sporulation rates, particularly at the highest salt concentration. Differences across leaf categories were observed in all parameters but fungal biomass, although the effects were not consistent across descriptors. All leaf categories responded with a similar intensity to salt contamination for all measured variables but sporulation rate. These results suggest that the deleterious influence of salt on litter decomposition occurs independently of the traits of the stream riparian subsidies.