抄録
Decomposition of fresh leaves of deciduous trees and colonization by macroinvertebrate shredders were studied in a mountain stream in Nagano Prefecture, central Japan. Decomposition experiments were carried out from late June to mid August ("summer experiment") and from early October to late November ("autumn experiment") in 1998. Two types of litter bag (9-mm mesh and 0.4-mm mesh) were used in these experiments to examine the role of shredders in leaf decomposition. Decomposition rates (ks) of fresh leaves calculated using an exponential decay model were faster (k=0.0073-0.0935) than most of the known rates for senescent leaves. The fresh leaves were subjected to a higher degree of microbial and shredder processing because of their lower C/N ratio. Decomposition rates in the summer experiment were higher than in the autumn experiment for both types of mesh bag. Decomposing activities of microbes and/or small shredders would have been higher in the summer experiment, when the C/N ratio of the leaves was lower and the stream temperature was higher. In the early stage of decomposition during the summer experiment, the biomass of shredders colonizing the coarse mesh bags was very large, due to colonization by many large, mature caddisfly larvae (i. e. Pseudostenophylax and Goerodes), while significant effects of mesh size on leaf decomposition were detected. These results suggest that in streams during early summer, when several shredder species are often at a mature stage even though coarse organic detritus is limited, input of high-quality fresh leaves is an important food resource for these shredders.
