Nitrate addition stimulates microbial decomposition of organic matter in salt marsh sediments
Nitrate addition stimulates microbial decomposition of organic matter in salt marsh sediments
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DOI：
10.1111/gcb.14726
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发表时间：
2019-07-17
影响因子：
11.6
通讯作者：
Bowen, Jennifer L.
中科院分区：
文献类型：
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作者：
Bulseco, Ashley N.;Giblin, Anne E.;Bowen, Jennifer L.
盐沼固碳的速度比陆地上的同类高出一个数量级以上，有助于减缓气候变化。随着氮主要以硝酸盐的形式继续流入沿海沃茨，目前还不清楚它将对这些高产系统的碳储存能力产生什么影响。这种不确定性在很大程度上是由硝酸盐在生物过程中可以发挥的双重作用驱动的，在生物过程中，它可以作为营养素刺激初级生产或促进异养代谢的有利电子受体。在这里，我们使用了一个受控的流通反应器实验来测试硝酸盐作为电子受体的作用，其对有机物分解和相关的微生物群落在盐沼沉积物的影响。有机物分解显着增加硝酸盐，即使在沉积物深度通常被认为是耐分解。同位素示踪剂的使用表明，这种模式在很大程度上是由刺激反硝化作用。硝酸盐的添加也显着改变了微生物群落，降低了α多样性，选择属于已知的减少硝酸盐和氧化更复杂形式的有机物的类群。傅立叶变换红外光谱进一步支持了这些结果，表明硝酸盐促进了复杂有机物质化合物分解成更多的生物可利用形式。综上所述，这些结果表明，存在的有机物池，只有成为访问硝酸盐，否则将保持稳定的沉积物。这种池的存在可能有重要的影响，碳储存，因为更大的分解率，氮负荷的增加可能会导致整体埋葬的有机丰富的沉积物。考虑到氮负荷沿着我们的海岸线的程度，我们必须更好地了解盐沼系统对养分富集的适应能力，特别是如果我们希望依靠盐沼和其他蓝碳系统进行长期碳储存。
Salt marshes sequester carbon at rates more than an order of magnitude greater than their terrestrial counterparts, helping to mitigate climate change. As nitrogen loading to coastal waters continues, primarily in the form of nitrate, it is unclear what effect it will have on carbon storage capacity of these highly productive systems. This uncertainty is largely driven by the dual role nitrate can play in biological processes, where it can serve as a nutrient-stimulating primary production or a thermodynamically favorable electron acceptor fueling heterotrophic metabolism. Here, we used a controlled flow-through reactor experiment to test the role of nitrate as an electron acceptor, and its effect on organic matter decomposition and the associated microbial community in salt marsh sediments. Organic matter decomposition significantly increased in response to nitrate, even at sediment depths typically considered resistant to decomposition. The use of isotope tracers suggests that this pattern was largely driven by stimulated denitrification. Nitrate addition also significantly altered the microbial community and decreased alpha diversity, selecting for taxa belonging to groups known to reduce nitrate and oxidize more complex forms of organic matter. Fourier Transform-Infrared Spectroscopy further supported these results, suggesting that nitrate facilitated decomposition of complex organic matter compounds into more bioavailable forms. Taken together, these results suggest the existence of organic matter pools that only become accessible with nitrate and would otherwise remain stabilized in the sediment. The existence of such pools could have important implications for carbon storage, since greater decomposition rates as N loading increases may result in less overall burial of organic-rich sediment. Given the extent of nitrogen loading along our coastlines, it is imperative that we better understand the resilience of salt marsh systems to nutrient enrichment, especially if we hope to rely on salt marshes, and other blue carbon systems, for long-term carbon storage.