LEAF LITTER DECOMPOSITION PROCESS ALONG THE PO RIVER: A MULTILEVEL APPROACH TO INVESTIGATE THE EFFECTS OF GLOBAL CLIMATE CHANGE

Leaf litter decomposition has been proposed as a useful approach to assess river ecosystems functionality. Since the occurrence of dry events is becoming increasingly frequent also in those streams that were previously considered perennial (Alpine streams for example) the aim of this study was to investigate to what extent leaf litter decomposition processes are affected by climate change. We adopted the leaf bags technique in four different sampling sites along the Po river and we assessed: mass loss during time, Ash-Free Dry Mass (AFDM), macroinvertebrates and microconsumers community diversity and composition. We expect that: i) leaf litter decomposition is more efficient in sampling sites where water was present during the whole experiment; ii) macroinvertebrate community is more diverse in the sites where dry events did not occur; iii) microconsumers are negatively affected by water loss because of desiccation. Microconsumers diversity is expected to be lower in sites that experienced dry phases and, consequently, coarse particulate organic matter degradation will be lower and less efficient; iv) there would be a sort of gradient from upstream to downstream: the site located above the tree line has a pristine stream condition, water would be present during the whole experiment and CPOM decomposition would be fast and efficient. Going downstream the situation would be clearly different, especially for the sampling sites located most downstream, where dry events are likely to occur, slowing down litter breakdown and leading to a poor macroinvertebrates and micronsumers community.