Threshold and multiple indicators for nitrogen saturation in subtropical forests.
Threshold and multiple indicators for nitrogen saturation in subtropical forests.
复制标题
DOI：
10.1016/j.envpol.2018.06.001
复制
发表时间：
2018-06
影响因子：
8.9
通讯作者：
Qian Yu;L. Duan;Longfei Yu;Xiao Chen;Gaoyue Si;Piaopiao Ke;Zhixiang Ye;J. Mulder
中科院分区：
文献类型：
--
作者：
Qian Yu;L. Duan;Longfei Yu;Xiao Chen;Gaoyue Si;Piaopiao Ke;Zhixiang Ye;J. Mulder
氮（N）沉降对森林生态系统的影响很大程度上取决于氮的状况。制定氮沉降极高的亚热带森林氮饱和阈值和实用指标，既可以加强森林管理，也可以加强对全球氮平衡和碳固存的评估。在这里，我们使用氮含量、C/N比和15N自然丰度（δ15N）作为氮饱和的潜在指标，量化了华南一些亚热带森林点的氮质量平衡并评估了当前的氮状况。在研究地点中，径流中的氮沉积量为 13.8 至 113kgN ha−1yr−1，且以铵 (NH4+) 为主。首次发现亚热带森林氮淋溶阈值为26–36kgN ha−1yr−1，比温带森林高160%（基于规定的最小值）。这表明氮沉降影响全球模型中的关键参数输入需要根据特定的生态系统特征进行修订。我们发现 O/A 层位的临界 C/N 比为 20，作为氮饱和度的指标。叶面氮含量和δ15N与氮沉降呈正相关，非常适合指示区域氮状况。 δ15N富集因子（Ɛfoli/So2、δ15Nfoliage- δ15NSoil2）在-10‰至-1‰之间，与其他氮沉降增加地区的趋势相似。这表明富集因子可用于研究森林生态系统中氮沉降的影响，无论氮输入δ15N的空间异质性、土壤氮有效性和地貌如何。
The influence of nitrogen (N) deposition on forest ecosystems largely depend on the N status. Developing threshold and practical indicators for N saturation in subtropical forests, with extremely high N deposition, would both enhance forest management and the assessments of global N balance and carbon (C) sequestration. Here, we quantified the N mass balance and assessed current N status at a number of subtropical forest sites in South China, using both N content, C/N ratio, and15N natural abundance (δ15N) as potential indicators of N saturation. Among the studied sites, N deposition ranged from 13.8 to 113 kg N ha−1yr−1in throughfall, and was dominated by ammonium (NH4+). The threshold for N leaching in subtropical forest was first found to be 26–36 kg N ha−1yr−1, which was 160% higher than in temperate forest (based on prescribed minimum). This indicates that critical parameter inputs in global models of the impact of N deposition are in need of revision, based on specific ecosystem characteristics. We found a critical C/N ratio of 20 for the O/A horizon as indicator of N saturation. Foliar N content and δ15N were positively correlated with N deposition and were well suited to indicate regional N status. The δ15N enrichment factor (Ɛfoli/So2, δ15Nfoliage- δ15NSoil2) was between −10‰ and −1‰, and had similar trend to those obtained from other regions with increasing N deposition. These suggest that the enrichment factor could be used to investigate the influence of N deposition in forest ecosystems, regardless of spatial heterogeneity in δ15N of N input, soil N availability and geomorphology.