Litter processing along a stream gradient: the role of invertebrates and decomposers

TLDR: Investigation of the processing of alder litter in 12 sites ranging from 2nd to 6th order in central Portugal during autumn/winter and spring/summer seasons found a pattern of shifting in processing vectors was observed, possibly because food was nonlimiting.

Abstract: Dissolved nutrients and temperature tend to increase in a downstream direction, whereas shredder density tends to decrease. As a result, the relative importance of microbes (bacteria and fungi) and invertebrates in leaf litter processing may gradually shift along a stream gradient. Therefore, we hypothesized that differences in litter decay between fine-mesh (invertebrates excluded) and coarse-mesh (accessible to invertebrates) bags will be high in low-order streams (i.e., 4). To test this hypothesis, we investigated the processing of alder (Alnus glutinosa) litter in 12 sites ranging from 2nd to 6th order in central Portugal during autumn/winter and spring/summer seasons. Mass loss rates (measured as % ash-free dry mass [AFDM]) were higher in spring/summer than in autumn/winter and higher in coarse- than in fine-mesh bags. No clear relationship was observed between river order and litter processing (% AFDM loss). In spring/summer, the difference in remain...