摘要 : We determined the trophic positions of 2 species of freshwater mussels, Elliptio dilatata and Ptychobranchus fasciolaris, from 2 small streams in central Ohio by measuring stable C and N isotope ratios and digestive fluid enzyme a... 展开 We determined the trophic positions of 2 species of freshwater mussels, Elliptio dilatata and Ptychobranchus fasciolaris, from 2 small streams in central Ohio by measuring stable C and N isotope ratios and digestive fluid enzyme activities. We also examined stable C and N isotopes, microbial biomass, microbial community structure, nutrient (i.e., C, N, and P) concentrations, and contribution of microbial C to total fine particulate organic C (FPOC). We hypothesized that 1) allochthonous inputs compose most of FPOC, 2) mussels use fine particulate organic material (FPOM) as a food source, and 3) mussels respond to the low-protein content of FPOM by showing high protease activity. Microbial C composed 35 to 86% of total FPOC during the autumn sampling period. FPOM stable isotope values varied seasonally, whereas delta(13)C and delta(15)N content in mussel tissue was spatially (i.e., among sites) and temporally similar. Mussels were 2 to 4parts per thousand more depleted in delta(13)C than seasonal FPOM. Digestive fluid enzymes were spatially and temporally stable across species, with activity of esterase > protease > lipase > glucosidase. Lipase:protease of digestive fluids from mussels were <1, indicating a low-protein diet. Our results suggest that microbial biomass in FPOM constitutes a large portion of mussel diet and that mussels assimilate significant amounts of C from this source. 收起