Mapping the leaf surface: Fine scale spatial patterns in microbial enzyme activity on decomposing leaves in streams
Kurt A. Smart and Colin R. Jackson. Department of Biology, The University of Mississippi, Shoemaker Hall, University, MS 38677
Leaf litter decomposition is a major component of carbon cycling in streams, and is mediated by microbial extracellular enzyme activity. As the leaf surface is spatially heterogeneous, spatial patterns in microbial activity on the litter surface should provide insights into fine-scale patterns in leaf-litter decomposition. Decomposing leaves of four species - sycamore, scarlet oak, northern red oak, and wild black cherry - were collected from a third order stream in northern Mississippi. Spatial variation in enzyme activity associated with individual leaves was measured by sampling 40-100 small discs (5 mm diameter) cut from each leaf. Discs were assayed for enzymes involved in lignin (peroxidase) and cellulose (beta-glucosidase and cellobiohydrolase) degradation. Peroxidase activity was similar across all leaf types and showed only modest levels of fine scale spatial variation. Beta-glucosidase and cellobiohydrolase activities were significantly greater on black cherry than the other leaf types, and were weakly correlated. Cellobiohydrolase showed greatest fine scale variation in activity for most leaves examined, often with 5-6x more activity in some patches than in others. These results show that fine scale spatial heterogeneity occurs on decomposing leaves, but the level of spatial variability varies with both leaf type and the microbial process involved.