Alteration of organic matter during infaunal polychaete gut passage and links to sediment organic geochemistry. Part I: Amino acids
Woulds, C.; Middelburg, J.J.; Cowie, G.L. (2012). Alteration of organic matter during infaunal polychaete gut passage and links to sediment organic geochemistry. Part I: Amino acids. Geochim. Cosmochim. Acta 77: 396-414. dx.doi.org/10.1016/j.gca.2011.10.042 In: Geochimica et Cosmochimica Acta. Elsevier: Oxford,New York etc.. ISSN 0016-7037; e-ISSN 1872-9533, more |  |
| Authors | | Top | - Woulds, C.
- Middelburg, J.J., more
- Cowie, G.L.
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| Abstract | Of the factors which control the quantity and composition of organic matter (OM) buried in marine sediments, the links between infaunal ingestion and gut passage and sediment geochemistry have received relatively little attention. This study aimed to use feeding experiments and novel isotope tracing techniques to quantify amino acid net accumulation and loss during polychaete gut passage, and to link this to patterns of selective preservation and decay in sediments. Microcosms containing either Arenicola marina or Hediste (formerly Nereis) diversicolor were constructed from defaunated sediment and filtered estuarine water, and maintained under natural temperature and light conditions. They were fed with C-13-labelled diatoms daily for 8 days, and animals were transferred into fresh, un-labelled sediment after similar to 20 days. Samples of fauna, microcosm sediment and faecal matter were collected after 8, similar to 20 and similar to 40 days, and analysed for their bulk isotopic signatures and C-13-labelled amino acid compositions. Bulk isotopic data showed that, consistent with their feeding modes, Hediste assimilated added C-13 more quickly, and attained a higher labelling level than Arenicola. Both species retained the added C-13 in their biomass even after removal from the food. A principal component analysis of C-13-labelled amino acid mole percentages showed clear differences in composition between the algae, faunal tissues, and sediment plus faecal matter. Further, the two species of polychaete showed different compositions in their tissues. The amino acids phenylalanine, valine, leucine, iso-leucine, threonine and proline showed net accumulation in polychaete tissues. Serine, methionine, lysine, aspartic and glutamic acids and tyrosine were rapidly lost through metabolism, consistent with their presence in easily digestible cell components (as opposed to cell walls which offer physical protection). All sample types (polychaete tissues, sediments and faecal matter) were enriched in labelled glycine. Possible mechanisms for this enrichment include accumulation through inclusion in tissues with long residence times, preferential preservation (i.e. selection against) during metabolism, production from other labelled amino acids during varied metabolic processes, and accumulation in refractory by-products of secondary bacterial production. Overall, similarities were observed between amino-acid decay patterns in faunated microcosms, afaunal controls, and those previously reported in marine sediments. Thus, while polychaete gut passage did produce compound-selective accumulation and losses of certain amino acids in polychaete tissues and faecal matter, the impact of polychaete gut passage on sediment organic geochemistry was difficult to deconvolve from microbial decay. Despite processing large volumes of organic matter, polychaetes may not have distinctive influence on sediment compositions, possibly because metabolic processes concerning amino acids may be broadly similar across a wide range of organisms. |
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