Microbial community structure in streams differs between leaf species with strongly contrasting breakdown rates

We examined microbial community structure of leaf species with contrasting breakdown rates in a small southeastern piedmont stream, by quantifying in situ litter breakdown and microbial succession on leaf packs of red maple and water oak (fast and slow decomposition, respectively) for 128 days. Breakdown was quantified as AFDM remaining, microbial biomass using phospholipid fatty acid analysis (PLFA), and relative abundance of fungal vs. bacterial biomass was compared between leaf species over time. Bacterial community structure was evaluated using denaturing gradient gel electrophoresis (DGGE) of 16SrDNA amplicons. Bacterial taxa present at all time points were preliminarily identified based on a small rDNA sequence, indicating a high diversity of genera (Collimonas sp., Nitrosospira sp., and Sphingopyxis sp.) on red maple over the study; in contrast, on water oak the bacterium Citrobacter freundii, a species known to degrade tannic acid, dominated on all dates. 16SrDNA clone libraries were constructed at multiple time points to examine bacterial community structure at greater phylogenetic resolution. On a given date, bacterial biomass was significantly higher on red maple than on water oak, whereas fungal biomass was higher on water oak. These data suggest strong differences in microbial communities among leaf species, which, in turn, may influence leaf species-specific breakdown rates in streams.