DECOMPOSITION OF LITTER OF SPARTINA ALTERNIFLORA IN A SALT MARSH ECOSYSTEM: BIOCHEMICAL AND GEOCHEMICAL STUDIES (LIGNIN, POLYSACCHARIDE, EXPORT)

This thesis describes a study of the changes in chemical composition of litter of Spartina alterniflora during decomposition and a characterization of the remains of vascular plant litter in coastal marine sediments of Buzzards Bay. The results were obtained through chemical analyses of litter, radioisotopic assays of ('14)C lignopolysaccharide mineralization, and determinations of the lignin and stable carbon isotope composition of samples of surface sediment from Buzzards Bay, Massachussetts.; The pattern of weight loss from S. alterniflora showed rapid loss during the first month, temperature-dependent decay during the first year, and little further loss during the second year. Structural carbohydrates underwent a similar pattern of loss. Hemicelluloses and cellulose disappeared from litter at approximately equal rates. After 9 months of decay, only 10% of the initial amounts of structural carbohydrates remained.; Litter of S. alterniflora initially contained substantial amounts of soluble phenolics, phenolics bound to cell walls, and lignins. Soluble phenolics were leached throughout decay. Initially some soluble phenolics may have become linked to plant cell walls; bound phenolics increased in one type of litter during the first month of decay. Lignins were lost at the slowest rate from litter, and increased in relative concentration during decay. Lignin and nitrogen concentrations were the parameters most closely correlated with decay of Spartina litter.; Mineralization of ('14)C lignopolysaccharides in laboratory experiments demonstrated that 10% of the ('14)C lignin moiety was degraded to ('14)CO(,2) during 1 month of incubation. The carbohydrate moiety within the lignopolysaccharide complex was mineralized 4 times faster than the lignin moiety, rendering the remaining material progressively more refractory and slowing decay rates of ('14)C lignopolysaccharides with time. Rates of mineralization of ('14)C lignopolysaccharides were similar to rates of lignopolysaccharide decomposition in litter in the marsh.; Results from lignin oxidation product analyses of sediments from Buzzards Bay indicated that vascular plant debris derived from nonwoody angiosperm tissues made up 5-10% of the total organic matter in these sediments. Model calculations suggested that export from salt marshes could account for a significant fraction of the vascular plant material in surface sediments in Buzzards Bay.