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

Abstract

Stable carbon isotope ratios of bacterial biomarkers were determined to infer sources 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 i15 : 0 and a15 : 0. Experiments showed that isotopic fractionation between substrate and biomarkers was relatively constant (Ϫ4 to Ϫ6‰, on average) compared to the wide range in 13 C/ 12 C ratios of carbon sources found in the studied marshes. At the Spartina site of the Waarde Marsh (The Netherlands), biomarker 13 C/ 12 C ratios were depleted by approximately 6‰ 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. Spartina contributed about half of the carbon in bacterial PLFA at the Kattendijke Marsh (The Netherlands) 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 comparison to local plant input, which in turn may differ among plant species.

Carbon and nitrogen cycling on intertidal mudflats of a temperate Australian estuary. III. Sources of organic matter

“…-15 to -19 ‰ at Site PC based on the isotopic composition of the branched 15:0 and 15:1 fatty acids (Table 4). MPB, then, are the most likely source of substrate to bacteria at Site CF, as found in other studies (Canuel et al 1997, Boschker et al 1999, Middelburg et al 2000. However, at Site PC, the contribution of material derived from Gracilaria sp.…”

“…Samples were coinjected twice with C 16 and C 24 deuterated n-alkanes of known isotopic composition; the average of the 2 injections is reported here. To obtain the ratio of the biomarker compounds, the carbon isotope ratio of the derivatised samples were corrected for the number of carbon atoms that had been added during derivatisation (3 for TMSi ethers and 1 for FAMEs) as described by Boschker et al (1999). Results are presented in standard δ notation as described above.…”

In situ experimental evidence of the fate of a phytodetritus pulse at the abyssal sea floor

“…Plasma-containing Foraminifera were hand-picked and identified, then decalcified and dried prior to determination of 12 C/ 13 C ratios. The remaining sediment was sliced in 0-2, 2-5, 5-10 cm, homogenized and sampled for bacterial biomass (cell counts), EEA of b-glucosidase and extraction of phospholipids [27][28][29] . Concentrations of fatty acid methyl esters were determined by gas chromatography-flame ionization detection.…”

The mineralogy of suspended matter, fresh and Cenozoic sediments in the fluvio-deltaic Rhine–Meuse–Scheldt–Ems area, the Netherlands: An overview and review

“…The algal matter will be less important in autumn and winter, which may more strongly change the isotopic value for suspended organic matter. Rather different values were observed by Boschker et al (1999) for a flat in the Eastern Scheldt: values around -20‰ irrespective of whether or not the site was vegetated. The difference between the two estuaries was attributed to differences in sedimentation rate and related burial of algal and non-algal organic matter.…”