The contribution of macrophyte-derived organic matter to microbial biomass in salt-marsh sediments Stable carbon isotope analysis of microbial biomarkers

摘要

Stable carbon isotope ratios of bacterial biomarkers were determined to infer souroes of organic carbon used by bacteria in the sediments of three salt marshes. Biomarkers studied were polar lipid-derived fatty acids (PLFA), mainly bacteria-specific, methyl-branched i 15 : 0 and al5 : 0. Experiments showed that isotopic fractionation between substrate and biomarkers was relatively constant (-4 to 6/1000, on average) compared to the wide range in 13C/12C ratios of carbon sources found in the studied marshes. At the Spartina site of the Waarde Marsh (The Netherlands), biomarker 13sC/12zC ratios were depleted by approximately 6/1000 more than expected for bacteria growing on Spartina litter and were similar to an unvegetated control sediment. This pattern suggested that local macrophyte production was of little importance and that other material (probably of algal origin) was the dominant carbon source for bacterial growth. Spariina contributed about half of the carbon in bacterial PLFA at the Kattendijke Marsh (The Netheriands) and dominated at the Great Marshes (U.S.). The variation in bacterial carbon sources in these marshes was probably related to estimated inputs of nonmacrophyte organic matter to the sediment. At the Waarde Marsh, a clear plant species effect was found as coupling between plant and bacteria was more important in Scirpus maritimus than in Spartina anglica. The contribution of local plant production to bacterial biomass in salt-marsh sediments is highly variable between marshes and depends on the input of nonmacrophyte material by sedimentation in compaln