Large Loss of Dissolved Organic Nitrogen from Nitrogen-Saturated Forests in Subtropical China
Large Loss of Dissolved Organic Nitrogen from Nitrogen-Saturated Forests in Subtropical China
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中国亚热带氮饱和森林溶解有机氮大量流失
DOI：
10.1007/s10021-008-9203-7
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发表时间：
2009-02-01
期刊：
影响因子：
3.7
通讯作者：
Yoh, Muneoki
中科院分区：
文献类型：
--
作者：
Fang, Yunting;Zhu, Weixing;Yoh, Muneoki
溶解有机氮（DON）最近被认为是陆地氮循环的重要组成部分，特别是在氮限制条件下，然而，增加大气氮沉降对森林土壤DON生产和损失的影响仍然存在争议。在这里，我们报告DON和溶解有机碳（DOC）的损失，从森林土壤接收非常高的长期环境大气氮沉降与或没有额外的实验N输入，调查DON地球化学N饱和条件下。我们研究了中国南方亚热带的一个古老的森林，一个年轻的松树林，和一个年轻的针阔混交林。所有这三种森林以前都被证明有很高的硝酸盐（NO3−）淋溶损失，其中最高的损失发生在古老的森林中。我们假设，DON淋溶损失将是森林的具体和最强的反应，实验N输入将在N饱和的古老的森林。我们的研究结果表明，在环境沉降（35-50 kg N ha− 1 y − 1作为穿透雨输入）下，所有三种森林中主要生根区以下的DON淋溶量都很高（6.5-16.9 kg N ha− 1 y −1）。在2.5年的试验投入50-150 kg N ha− 1 y −1后，DON淋失增加了35-162%。肥料驱动的DON淋溶增加占添加N的4-17%。DOC损失的同时增加，观察到只有在松树林，即使DOC：DON比例下降，在所有三个森林。我们的数据表明，DON占23-38%的总溶解N淋溶，强调DON可能是一个重要的途径，从森林走向N饱和的N损失。最显着的N处理DON通量的影响没有发现在原始森林，在环境条件下的DON损失最高。在所有三个森林中，DON淋溶与NO3-淋溶高度相关。我们推测，过量NO3-（通过化学反应NO2-）进入土壤有机质的非生物结合和随后产生的富氮溶解有机质是中国南方亚热带森林氮饱和的持续和大量DON损失的主要机制。
Dissolved organic nitrogen (DON) has recently been recognized as an important component of terrestrial N cycling, especially under N-limited conditions; however, the effect of increased atmospheric N deposition on DON production and loss from forest soils remains controversial. Here we report DON and dissolved organic carbon (DOC) losses from forest soils receiving very high long-term ambient atmospheric N deposition with or without additional experimental N inputs, to investigate DON biogeochemistry under N-saturated conditions. We studied an old-growth forest, a young pine forest, and a young mixed pine/broadleaf forest in subtropical southern China. All three forests have previously been shown to have high nitrate (NO3−) leaching losses, with the highest loss found in the old-growth forest. We hypothesized that DON leaching loss would be forest specific and that the strongest response to experimental N input would be in the N-saturated old-growth forest. Our results showed that under ambient deposition (35–50 kg N ha−1y−1as throughfall input), DON leaching below the major rooting zone in all three forests was high (6.5–16.9 kg N ha−1y−1). DON leaching increased 35–162% following 2.5 years of experimental input of 50–150 kg N ha−1y−1. The fertilizer-driven increase of DON leaching comprised 4–17% of the added N. A concurrent increase in DOC loss was observed only in the pine forest, even though DOC:DON ratios declined in all three forests. Our data showed that DON accounted for 23–38% of total dissolved N in leaching, highlighting that DON could be a significant pathway of N loss from forests moving toward N saturation. The most pronounced N treatment effect on DON fluxes was not found in the old-growth forest that had the highest DON loss under ambient conditions. DON leaching was highly correlated with NO3−leaching in all three forests. We hypothesize that abiotic incorporation of excess NO3−(through chemically reactive NO2−) into soil organic matter and the consequent production of N-enriched dissolved organic matter is a major mechanism for the consistent and large DON loss in the N-saturated subtropical forests of southern China.