Vertical Changes in the Flux of Atmospheric Nitrate From a Forest Canopy to the Surface Soil Based on Δ17O Values
Vertical Changes in the Flux of Atmospheric Nitrate From a Forest Canopy to the Surface Soil Based on Δ17O Values
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DOI：
10.1029/2020jg005876
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发表时间：
2021-03
期刊：
影响因子：
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通讯作者：
Takahiro Inoue;F. Nakagawa;H. Shibata;U. Tsunogai
中科院分区：
文献类型：
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作者：
Takahiro Inoue;F. Nakagawa;H. Shibata;U. Tsunogai
为了更好地了解控制森林流域N保留和N输出的因素，有必要了解大气氮沉降、植物-土壤系统内部氮循环和N淋溶之间的关系。大气硝酸盐（NO3−atm）和微生物硝化作用产生的再矿化硝酸盐对水体总硝酸盐（NO3−）的相对贡献已经得到了很多研究。然而，这两种类型的NO3−从森林冠层到土壤的动态尚不清楚。因此，我们确定了在日本北部天然针叶阔叶混交林中，NO3 -通量和NO3 - 17O过量（Δ17O）的变化，NO3 -是NO3 - atm的强大示踪剂，从大量沉积到栎树、云杉以及矮竹主导的冠层间隙的土壤水分。NO3−通过森林地表后，Δ17O值急剧下降，说明NO3−淋滤的主要来源是森林地表的硝化作用。NO3−atm通量在整体沉降和透雨之间显著减少，特别是在栎树和云杉中，这表明林冠是NO3−atm的重要汇。林隙中栎树（86.3±10.1%）和云杉（87.7±8.8%）对NO3−atm的截留量高于杉树（49.9±26.6%）。我们的研究表明，Δ17O NO3−值是量化复杂森林N循环中大气硝酸盐动态的一个有前途的工具。
To better understand the factors that control N retention and N export in forested watersheds, it is necessary to understand the relationships among atmospheric nitrogen (N) deposition, internal N cycling within plant‐soil systems, and N leaching. The relative contributions of atmospheric nitrate (NO3−atm) and remineralized nitrate produced by microbial nitrification to total nitrate (NO3−) in stream water have been investigated in many studies. However, the dynamics of these two types of NO3− from the forest canopy to the soil are not well understood. Therefore, we determined the changes in the NO3− flux and the 17O excess (Δ17O) of NO3−, a robust tracer of NO3−atm, from bulk deposition to the soil water beneath oak and spruce trees as well as dwarf bamboo‐dominated canopy gaps in a natural coniferous‐broadleaved mixed forest in northern Japan. The Δ17O values in NO3− dramatically decreased after passing through the forest floor, indicating that the dominant source of NO3− leaching is nitrification in the forest floor. In contrast, a large decrease in NO3−atm flux was observed between bulk deposition and throughfall, especially for oak and spruce, suggesting that the forest canopy is an important sink for deposited NO3−atm. The retention of NO3−atm by the canopy was higher for oak (86.3 ± 10.1%) and spruce (87.7 ± 8.8%) than for Sasa in the canopy gap (49.9 ± 26.6%). Our study demonstrated that the Δ17O value of NO3− is a promising tool for quantifying the atmospheric nitrate dynamics in complex forest N cycling.