Microbial colonization, respiration, and breakdown of maple leaves along a stream-marsh continuum

Breakdown rates, macroinvertebrate and bacterial colonization, and microbial respiration were measured on decaying maple (Acer saccharum) leaves at three sites along a stream-marsh continuum. Breakdown rates (-k ±SE) were 0.0284±0.0045 d^-1 for leaves in a high-gradient, non-tidal stream; 0.0112±0.0019 d^-1 for leaves at the confluence of the stream with a tidal, freshwater marsh; and 0.0062±0.0009 d^2-1 for leaves in the tidal, freshwater marsh. Breakdown rates were significantly faster (ANCOVA, F<0.008) at the high-gradient, non-tidal stream site and at the tidal stream site than in the tidal marsh. Macroinvertebrate density on decaying leaves was low at all sites (<7 organisms g^-1 AFDM leaf mass) and was dominated by chironomids and amphipods. Bacterial density on decaying leaves ranged from 8.56 × 10⁸ CFU g^-1 AFDM leaf mass to 13.38 × 10⁸ CFU g^-1 AFDM. Cumulative microbial respiration, calculated as the product of mean respiration on a sampling date, days in the interval preceding the sampling date, and hours per day, accounted for 34.3±6.0%, 53.0±4.8%, and 51.5±7.9% of the leaf mass loss (as carbon) at these sites. Although the breakdown rate was fastest at the non-tidal stream site, significantly less leaf mass was lost through microbial respiration. Most mass loss from leaves at this site was probably due to physical processing associated with stream habitats.