Leaf breakdown and the ecosystem functioning of alpine streams

Abstract

AbstractLeaf breakdown, a key functional process, was examined in 3 glacial streams, 3 alpine springbrooks, and a rock-glacier stream in the Swiss Alps. Environmental conditions within each stream type were expected to significantly affect leaf breakdown rates among streams. Individual leaf packs (7 g fresh mass) of alder (Alnus viridis) were immersed in each stream and replicate samples were collected at periodic intervals over 49 d. Collected leaves were assessed for N and P, ergosterol (a measure of fungal biomass), % lignin (an indicator of recalcitrance), and aquatic macroinvertebrates. Leaf breakdown was faster in the springbrooks (k = −0.0085) and rock-glacier stream (k = −0.0073) than in the glacial streams (k = −0.0027) when expressed in terms of time. However, leaf breakdown rates based on degree days were similar among streams, ranging from k = −0.0011 to −0.0020. Leaf P levels increased over time in all sites, and reflected respective increases in ergosterol. Leaf ergosterol levels increased f...