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Decomposition in salt marsh ecosystems: The phases and major factors affecting disappearance of above-ground organic matter


Decay of litter of salt marsh grasses occurs in three phases. First there is an early phase lasting less than a month, with fast rates of weight loss, during which 5 to 40% of the litter is lost, probably by leaching of soluble compounds. A second slower phase lasts up to a year. In this second phase, microbial degradation of organic matter and subsequent leaching of hydrolyzed substances remove an additional 40 to 70% of the original material. A third phase may last an additional year; in this phase decay is very slow because only relatively refractory materials remain. By this third stage as little as 10% of the original material may remain. Differences in the chemical makeup of litter are the major factors affecting the amount of decay during the leaching and decomposer phases. Such chemical differences may be due to differences in the chemistry of the plant species producing the litter or in nutrient supply. Spartina patens (Ait.) Muhl., for example, produces litter that decays more slowly than that of S. alterniflora Loisel. Increases in internal nitrogen content of litter increase loss of weight during the leaching and decomposer phases, while the external supply of nitrogen increases decay rates only during the decomposer phase. Temperature increases decay rates to some extent during the decomposer phase. The feeding activity of large detritus-feeding invertebrates produces a small but significant increase in decay rate during the decomposer phase. Decay rate in litterbags mimics decay of litter in the field, and makes possible estimates of litter turnover. The turnover of litter of S. alterniflora was 1.1-1.4 · yr-1. Litter of S. patens turns over more slowly, 2.1 · yr-1. Nutrient enrichment accelerates turnover of litter up to 24% compared to control litter. Since eutrophication of salt marshes both enriches litter and changes species of plants, it has broad consequences for ecological processes dependent on decomposition of organic matter. © 1985.

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