MICROBIAL DEGRADATION OF DETRITAL LIGNOCELLULOSES IN MARINE AND FRESHWATER ECOSYSTEMS (GEORGIA, FLORIDA, LIGNIN, WETLAND, DECOMPOSITION)

Vascular plants contribute significant quantities of particulate organic carbon to wetland ecosystems in the form of lignocellulosic detritus. Methodology for preparing specifically radiolabeled ('14)C-(lignin)-lignocellulose and ('14)C-(polysaccharide)-lignocellulose derived from a variety of herbaceous, aquatic macrophytes was optimized by using ('14)C-cinnamic acid as a precursor of lignin and ('14)C-glucose as a precursor of polysaccharides. These specifically radiolabeled lignocelluloses were utilized in studies of the biogeochemical transformations and fate of carbon from the lignin and polysaccharide components of lignocellulose in sediments from a salt marsh, mangrove swamp, and the Okefenokee Swamp. Differences in the biodegradability of lignocelluloses derived from a grass, sedge, rush, and wood were observed; lignocelluloses derived from herbaceous plants were degraded faster than lignocelluloses from woody plants. Typically, 20 to 30% of the polysaccharide component and 5 to 10% of the lignin component of lignocelluloses were mineralized during laboratory incubations lasting 25 days. The polysaccharide component of lignocelluloses was degraded 2 to 5 times faster than the lignin component of lignocelluloses, resulting in the gradual enrichment of the lignocellulose in lignin with time. Unlike terrestrial ecosystems in which fungi are believed to be the primary degraders of lignocellulose, bacteria appear to be the primary degraders of lignin and lignocellulose in marine ecosystems. Degradation rates of lignocelluloses were similar in sediments from a Georgia salt marsh and a mangrove swamp located on Andros Island, Bahamas. However, aerobic degradation rates of lignocellulose were much lower in sediments from the Okefenokee Swamp, a peat accumulating environment, than in salt marsh or mangrove swamp sediments. The acidity (pH 3.8) of Okefenokee Swamp water appeared to contribute to the low degradation rates of lignocellulose. Anaerobic biodegradation rates of lignocelluloses were also highly dependent on the source of the lignocellulose and the environment from which anoxic sediments were collected. In anoxic sediments from marine ecosystems, lignocelluloses were degraded anaerobically at rates from 2 to 10% of the aerobic degradation rates. In anoxic sediments from the Okefenokee Swamp, lignocelluloses were degraded anaerobically at approximately 35% of the aerobic degradation rate. Contrary to previous investigations, the lignin component of lignocelluloses was biodegradable in the absence of oxygen.