Changes in compound specific ¦Ä¹⁵N amino acid signatures and d/l ratios in marine dissolved organic matter induced by heterotrophic bacterial reworking

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• 作者：M.Ll. Calleja ; ^{marialluch.calleja@gmail.com} ; F. Batista ; M. Peacock ; R. Kudela ; M.D. McCarthy
• 关键词：Marine dissolved organic matter ; Marine dissolved organic nitrogen ; Amino acids ; Compound specific nitrogen stable isotopes ; Bacterial degradation
• 刊名：Marine Chemistry
• 出版年：2013
• 出版时间：20 February, 2013
• 年：2013
• 卷：149
• 期：Complete
• 页码：32-44
• 全文大小：767 K

文摘

Compound-specific ¦Ä¹⁵N analysis of individual amino acids (¦Ä¹⁵N-AA) represents a potentially important new tool which may reveal the molecular-level basis for ¦Ä¹⁵N signature of dissolved organic nitrogen (DON) in the ocean, as well indicate DON sources and specific mechanisms of alteration. Past work has indicated that ¦Ä¹⁵N-AA may be effective at indicating the effects of microbial heterotrophy, however the influence of bacterial degradation on ¦Ä¹⁵N-AA patterns has never been directly investigated. Here we measured molecular-level changes in ¦Ä¹⁵N-AA patterns in freshly produced algal high molecular weight (HMW) DON due to heterotrophic bacterial reworking, together with linked changes in enantiomeric (D vs. L) AA ratios and also the AA molar percentage-based degradation index (DI). Our results show a strong increase in degradation with microbial consumption of dissolved organic carbon (DOC), consistent with previous studies. The ¦Ä¹⁵N-AA data show systematically higher ¦Ä¹⁵N values for most individual AA after DOC bacterial reworking, resulting in average increases of 3-6¡ë in ¦Ä¹⁵N of total proteinaceous material. The average deviation in the ¦Ä¹⁵N values of all AA (¦²V parameter) also increased with degradation, indicating an increase in ¦Ä¹⁵N-AA pattern complexity, most likely due to selected microbial resynthesis of specific AA. These results show that ¦Ä¹⁵N-AA patterns have the ability to directly track the effects of microbial resynthesis in DON. They indicate that ¦Ä¹⁵N-AA represents a highly specific tracer that provides independent, and yet strongly complimentary, information vs. existing AA-based degradation indicators. Together, our data suggests that heterotrophic microbial degradation in the ocean would be expected to increase ¦Ä¹⁵N values of the oceanic DON pool vs. autotrophic sources. This conclusion is consistent with recent results on ¦Ä¹⁵N signatures of total and HMWDON pool in the open sea, however it also strongly implicates bacterial sources as the likely mechanism for ¦Ä¹⁵N-DON changes. Reevaluating existing DON isotopic data in light of these results may improve our understanding of the influence and mechanism of bacterial reworking on DON long-term preservation in the marine water column.