Breaking it Down: Shredder Influence on Microbial Diversity during Leaf Breakdown

Organic matter decomposition rates in streams can be influenced by initial resource quality, hydrology and colonizing communities. We used Terminal Restriction Fragment Length Polymorphism (T-RFLP) to assess microbial communities in decomposing leaves of two temperate ( Acer rubrum  and  Quercus prinus ) and two tropical ( Dacryodes excelsa  and  Cecropia schreberiana ) leaf species while in the presence or absence of a common temperate-zone shredder. By identifying fragments in each sample, we analyzed microbial diversity by estimating richness, Shannon’s diversity, and evenness. We hypothesized that consumers would alter microbial diversity on leaf substrates throughout different stages of breakdown. Percent leaf mass remaining significantly differed with consumers present (df=1,P=0.01) as well as by leaf type (df=3,P=<0.001). Evenness of bacteria and fungi were not significantly different for either treatment group. Further, bacteria richness (df=1,P=0.005) and Shannon’s diversity (df=1,P=0.007) were only significantly different between consumer treatments. Fungi richness (df=3,P=<0.001) and Shannon’s diversity (df=3,P=0.01) were only significantly different between leaf type treatments. These results suggest that the presence of consumers and leaf identity are driving forces in the diversity of microbial communities on leaf substrates during leaf breakdown.