Chronic nitrogen deposition influences the chemical dynamics of leaf litter and fine roots during decomposition
Chronic nitrogen deposition influences the chemical dynamics of leaf litter and fine roots during decomposition
复制标题
DOI：
10.1016/j.soilbio.2017.04.011
复制
发表时间：
2017-09-01
影响因子：
9.7
通讯作者：
Pregitzer, Kurt S.
中科院分区：
文献类型：
--
作者：
Xia, Mengxue;Talhelm, Alan F.;Pregitzer, Kurt S.
大气氮沉降在北方半球的大部分地区引起森林碳汇，这种碳汇可能部分是由于凋落物分解较慢。尽管微生物对实验性氮沉积的反应已经得到了充分的研究，但将这些微生物反应与腐烂垃圾中特定化合物降解变化联系起来的证据却很少。我们使用湿化学和傅里叶变换红外光谱（FTIR）的方法来研究在为期三年的分解实验中，在美国中北部的四个北方阔叶林的落叶和细根化学的慢性模拟氮沉降的影响。凋落叶和细根的初始化学，如酸不溶性部分（AIF，或Klason木质素）和缩合单宁（CT）的浓度是非常不同的。这些最初的差异在分解过程中一直存在。重量测定法定义的AIF和木质素/碳水化合物参考IR峰比率都提供了在模拟氮沉降下细根中的木质素被选择性地保存的证据。木质素/碳水化合物峰比率与AIF强烈相关，表明AIF是木质素的良好预测因子。由于AIF是丰富的细根，较慢的AIF降解的主要驱动力的细根分解缓慢增氮下，解释73.5%的额外的根质量保留。增氮还减缓了细根中CTs和蛋白质的损失。氮添加最初减缓了AIF，CTs和蛋白质在凋落叶中的损失，这是相对较低的AIF，但这些影响在后期消失，并没有影响凋落叶质量损失在实验期间。我们的研究结果表明，分解的化学类受到氧化降解，如木质素和CT，一般抑制氮富集，但这种抑制是否最终减缓凋落物质量损失，并导致有机质积累取决于这些类在凋落物的初始数量。(C)2017作者爱思唯尔有限公司出版
Atmospheric nitrogen deposition induces a forest carbon sink across broad parts of the Northern Hemisphere; this carbon sink may partly result from slower litter decomposition. Although microbial responses to experimental nitrogen deposition have been well-studied, evidence linking these microbial responses to changes in the degradation of specific compounds in decaying litter is sparse. We used wet chemistry and Fourier transform infrared spectroscopy (FTIR) methods to study effects of chronic simulated nitrogen deposition on leaf litter and fine root chemistry during a three-year decomposition experiment at four northern hardwood forests in the north-central USA. Leaf litter and fine roots were highly different in initial chemistry, such as concentrations of acid-insoluble fraction (AIF, or Klason lignin) and condensed tannins (CTs). These initial differences persisted over the course of decomposition. Gravimetrically-defined AIF and lignin/carbohydrate reference IR peak ratios both provide evidence that lignin in fine roots was selectively preserved under simulated nitrogen deposition. Lignin/carbohydrate peak ratios were strongly correlated with AIF, suggesting that AIF is a good predictor of lignin. Because AIF is abundant in fine roots, slower AIF degradation was the major driver of the slower fine root decomposition under nitrogen enrichment, explaining 73.5% of the additional root mass retention. Nitrogen enrichment also slowed the loss of CTs and proteins in fine roots. Nitrogen additions initially slowed the loss of AIF, CTs, and proteins in leaf litter, which was comparatively low in AIF, but these effects disappeared at the later stage and did not affect leaf litter mass loss during the experiment. Our results suggest that decomposition of chemical classes subject to oxidative degradation, such as lignin and CTs, is generally inhibited by nitrogen enrichment; but whether this inhibition eventually slows litter mass loss and leads to organic matter accumulation depends on the initial quantities of these classes in litter. (C) 2017 The Authors. Published by Elsevier Ltd.