| The microbial ecology of two wetland ecosystems in southeastern Georgia, U.S.A., was studied with respect to microbial community dynamics and microbially-mediated transformations of vascular plant detritus. In the Okefenokee Swamp, biomass of microorganisms in the water column and sediments was generally lower in winter months and higher during spring and summer. Biomass and activity (measured as {dollar}sp{lcub}14{rcub}{dollar}C-lignocellulose mineralization) differed significantly among five habitats within the Okefenokee, and also among locations within each habitat. Significant heterogeneity in the structure of Okefenokee microbial communities was found at scales from 30 cm to 150 m. In field and laboratory studies of vascular plant decomposition in the Okefenokee and a salt marsh on Sapelo Island, the mathematical model which best describes decomposition kinetics is the "decaying coefficient" model. This model accommodates the changes in quality of vascular plant detritus resulting from preferential decomposition of more labile fractions (e.g., non-lignocellulosic material and holocellulose) and the relative accumulation of more refractory moieties (e.g., lignin). Laboratory decomposition data, which were more highly resolved than field data and free of effects of fluctuating environmental conditions, were fit best by a "composite decaying coefficient" model, which considers the detritus to be composed of several chemically distinct fractions in addition to allowing for gradual decreases in specific decomposition rates of each fraction as material ages. A simulation model was used to predict the fate of carbon derived from lignocellulose in the food web of a marsh community in the Okefenokee Swamp. The efficiency of transfer of lignocellulosic carbon through the microbial loop is low, and overall only 5% of the carbon used by bacteria and fungi is predicted to be consumed subsequently by metazoans. Furthermore, less than 4% of the biomass of larger detritivorous animals can be traced to carbon from lignocellulose. Detritus food webs based on other, less abundant, sources of detrital carbon such as dissolved organic carbon, or perhaps classical plant-herbivore food webs, are more likely to be the major source of metazoan production in this ecosystem. |
