The relative importance of exogenous and substrate-derived nitrogen for microbial growth during leaf decomposition.
The relative importance of exogenous and substrate-derived nitrogen for microbial growth during leaf decomposition.
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外源氮和底物来源的氮对于叶片分解过程中微生物生长的相对重要性。
DOI：
10.1890/12-1339.1
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发表时间：
2013
期刊：
影响因子：
4.8
通讯作者：
Steven A. Thomas
中科院分区：
文献类型：
--
作者：
B. Cheever;Jackson R. Webster;E. E. Bilger;Steven A. Thomas
定殖在碎屑上的异养微生物通过从其基质中吸收氮或固定外源无机氮来获得生长所需的氮。在全球生物有效氮增加的情况下，微生物利用这两个库对氮循环和有机质分解有不同的影响。我们使用糖枫叶标记15 N来区分微生物N已被同化的叶基板（富含15 N）或固定的水（天然丰度15 N：14 N）在五个阿巴拉契亚溪流环境NO3（-）N浓度范围从约5到900微克NO3（-）N/L。环境NO3（-）浓度增加糖枫分解速率，但不影响来自基质或外源库的微生物氮比例。相反，这些比例的强烈影响的碎屑无灰干质量（AFDM）剩余的百分比。在所有的流的第一个24小时后，基板衍生的N构成了很大比例的微生物N。碎屑和微生物的同位素15 N签名接近的水分解的进展，在所有的流，这表明外源N可能是主要的N源，即使外源N浓度低，以满足微生物的要求。我们的研究结果支持更快速的有机物分解的预测，以响应增加氮的可用性，并强调驱动微生物氮循环和有机物分解的过程的紧密耦合。
Heterotrophic microbes colonizing detritus obtain nitrogen (N) for growth by assimilating N from their substrate or immobilizing exogenous inorganic N. Microbial use of these two pools has different implications for N cycling and organic matter decomposition in the face of the global increase in biologically available N. We used sugar maple leaves labeled with 15N to differentiate between microbial N that had been assimilated from the leaf substrate (enriched with 15N) or immobilized from the water (natural abundance 15N:14N) in five Appalachian streams ranging in ambient NO3(-)N concentrations from about 5 to 900 microg NO3(-)N/L. Ambient NO3(-) concentration increased sugar maple decomposition rate but did not influence the proportion of microbial N derived from substrate or exogenous pools. Instead, these proportions were strongly influenced by the percentage of detrital ash-free dry mass (AFDM) remaining. Substrate-derived N made up a large proportion of the microbial N after the first 24 h in all streams. Detrital and microbial isotopic 15N signatures approached that of the water as decomposition progressed in all streams, suggesting that exogenous N may be the predominant source of N for meeting microbial requirements even when exogenous N concentrations are low. Our results support predictions of more rapid decomposition of organic matter in response to increased N availability and highlight the tight coupling of processes driving microbial N cycling and organic matter decomposition.