Temperate streams are subsidized by inputs of leaf litter peaking in fall. Yet, stream communities decompose dead leaves and integrate their energy in the aquatic food web throughout the whole year. Most studies investigating stream decomposition largely overlook long-term trajectories, which must be understood for an appropriate temporal upscaling of ecosystem processes. Using mesocosms, we quantified changes in carbon, nitrogen and phosphorus content of three leaf species during decomposition at weekly to multi-month intervals for up to a year; then, we tested how decomposition duration affected the subsequent consumption by a keystone amphipod macroinvertebrate. Over a year, nitrogen and phosphorus percentage increased across all leaf species, but only the recalcitrant species maintained initial levels of absolute nitrogen and phosphorus. Prolonged decomposition barely affected or impaired amphipod consumption of labile leaf species, whereas it enhanced feeding on the recalcitrant species. Overall, we demonstrate that recalcitrant leaves might serve as longer-stored potential resources for when labile species have already been consumed, and that their increasing palatability observed over multi-month intervals of sustained decomposition may stabilize fluctuations in the rates of leaf litter integration into aquatic food webs. This year-long perspective highlights the relevancy of slow-decomposing leaves for aquatic detrital communities.

Funding is from the Swiss Federal Office for Environment (FOEN/BAFU), the University of Zurich Research Priority Programme Global Change and Biodiversity, and the Swiss National Science Foundation.