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.

中文翻译：

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基于Δ17O值的森林冠层至表层土壤的硝态氮通量的垂直变化

为了更好地了解控制森林流域中氮保留和氮出口的因素，有必要了解大气氮（N）沉积，植物-土壤系统中内部氮循环以及氮淋失之间的关系。大气硝酸盐（NO的相对贡献₃ ^-_大气压）和由微生物产生的硝化成硝酸盐总再矿化硝酸盐（NO ₃ ^- ）的流水已在很多研究了研究。然而，这两种类型的NO的动力学₃ ^-从树冠到土壤还不是很清楚。因此，我们决定在NO的变化₃ ^-通量和¹⁷ ø过量（Δ ¹⁷NO的O）₃ ^-，NO的稳健示踪剂₃ ^-_大气压，从大容量沉积橡树和云杉树以及矮竹为主的冠空隙下的土壤中的水以自然的针叶阔叶混交林日本北部。的Δ ^17个中的NO O值₃ ^-穿过森林地面后显着降低，这表明NO的主要来源₃ ^-浸出是在森林地板硝化。相反，NO ₃ ^- _atm的大量减少观察到大量沉积物和穿透物之间的通量，特别是对于橡树和云杉而言，表明林冠层是沉积NO ₃ ^- _atm的重要汇。橡木（86.3±10.1％）和云杉（87.7±8.8％）对冠层间隙中NO ₃ ^- _atm的保留高于Sasa（49.9±26.6％）。我们的研究表明，Δ ¹⁷ NO的O值₃ ^-是用于复杂森林氮循环量化大气硝酸盐动力学有希望的工具。