Combined effects of salinization and temperature on microbial-mediated oak decomposition and invertebrate consumption

Water salinization is a recognized growing threat to freshwaters, whose consequences on streams' function, per se or concomitantly with other stressors, are still far from clear. This microcosm study evaluated the combined effect of salinization (0 and 4 g/l NaCl) and temperature (5, 15, and 20 degrees C) on microbial-mediated oak leaf litter decomposition, with fungal biomass, sporulation, and microbial respiration as microbial descriptors. Invertebrate consumption was also assessed using the common shredder Sericostoma vittatum (Trichoptera, Sericostomatidae). Mass loss was affected by temperature and interaction between salinity and temperature. Under salt conditions, mass loss was higher at 15 degrees C and reduced ( 10%) at 20 degrees C. Microbial activity was lower at 5 degrees C and higher at 15 and 20 degrees C, irrespective of salinity. Fungal biomass was affected by both temperature (5 < 20 < 15 degrees C) and salinity (4 < 0 g/l NaCl), although the interaction between both was not significant. The interaction of both variables affected the production of spores: salt addition strongly reduced sporulation rates at all temperatures despite a significant increase in conidial production with temperature. Invertebrate leaf consumption was significantly reduced only by salinization. Overall, our results seem to indicate that temperature may modulate the effect of salinization (at least at >= 4 g/l NaCl) on stream leaf decomposition. While stronger salinization effects may be observed at higher temperatures, a consistent strong inhibition of shredders' feeding behavior promoted by salt, regardless of temperature, may anticipate important repercussions on streams' secondary production throughout the year.