Abstract
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.
Highlights
Primary production by salt marsh vegetation can be very high, reaching 4-5 kg *m- 2. yr- l (Valiela et al, 1976), but only a few percent of the annual aboveground production is consumed by herbivores (Teal, 1962)
In this paper we describe the use of litterbags and various experimental procedures in the field to manipulate the time that litter was under water, vary the initial percent nitrogen in the litter and the nitrogen concentration in the environment where litter was decaying, and set up experiments that excluded large invertebrate detritus-feeders
Rinsing sediment off the 19.5-month-old litter removed between about half the dry weight found in litterbags retrieved from creekbanks and 4% of the weight of litterbags from high marsh (Table I)
Summary
Primary production by salt marsh vegetation can be very high, reaching 4-5 kg *m- 2. yr- l (Valiela et al, 1976), but only a few percent of the annual aboveground production is consumed by herbivores (Teal, 1962). Primary production by salt marsh vegetation can be very high, reaching 4-5 kg *m- 2. In a New England salt marsh, an amount of organic matter equivalent to z 20 y0 of the above-ground production is removed annually from the marsh surface by tidal flushing (Valiela et al, 1982). About 5 % of the annual production accumulates below ground as peat (Valiela & Teal, 1979). In view of the relatively high rates of primary production, decomposition has to be a very active process in salt marsh ecosystems. The relatively small herbivore consumption means that most of the annual production in salt marshes becomes litter and detritus, and this dominance of the detrital path of organic matter over the herbivore path makes salt marshes a suitable environment to study interactions between decomposers and detritus
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