The boreal forest is one of the world's largest terrestrial biome and plays crucial roles in global biogeochemical cycles, such as carbon (C) sequestration in vegetation and soil. However, the impacts of decades of N deposition on N-limited ecosystems, like the eastern Canadian boreal forest, remain unclear. For 13 years, N deposition was simulated by periodically adding ammonium nitrate on soils of two boreal coniferous forests (i.e., balsam fir and black spruce) of eastern Canada, at low (LN) and high (HN) rates, corresponding to 3 and 10 times the ambient N deposition, respectively. We show that more than a decade of N addition had no strong effects on mineral soil C, N, P, and cation concentrations and on foliar total Ca, K, Mg, and Mn concentrations. In organic soil, C stock was not affected by N addition while N stock increased, and exchangeable Ca²⁺ and Mg²⁺ decreased at the balsam fir site under HN treatment. At both sites, LN treatment had nearly no impact on foliage and soil chemistry but foliar N and N:P significantly increased under HN treatment, potentially leading to foliar nutrient imbalance. Overall, our work indicates that, in the eastern Canadian boreal forest, soil and foliar nutrient concentrations and stocks are resilient to increasing N deposition potentially because, in the context of N limitation, extra N would be rapidly immobilized by soil micro-organisms and vegetation. These findings could improve modeling future boreal forest soil C stocks and biomass growth and could help in planning forest management strategies in eastern Canada.

中文翻译：

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加拿大东部北方森林土壤和叶面化学显示出对长期氮添加的恢复能力

北方森林是世界上最大的陆地生物群落之一，在全球生物地球化学循环中发挥着至关重要的作用，例如植被和土壤中的碳 (C) 固存。然而，数十年的氮沉积对加拿大东部北方森林等有限氮生态系统的影响仍不清楚。 13年来，通过在加拿大东部的两种北方针叶林（即香脂冷杉和黑云杉）的土壤中定期添加硝酸铵来模拟氮沉降，分别以低（LN）和高（HN）比率添加，对应于3和10分别是环境氮沉积的倍数。我们发现，十多年来的氮添加对矿质土壤 C、N、P 和阳离子浓度以及叶面总 Ca、K、Mg 和 Mn 浓度没有强烈影响。在有机土壤中， HN处理香脂杉场地的C库不受施氮影响，而N库增加，交换性Ca ²⁺和Mg ²⁺减少。在这两个地点，LN 处理对叶子和土壤化学几乎没有影响，但 HN 处理下叶面的 N 和 N:P 显着增加，可能导致叶面养分失衡。总体而言，我们的工作表明，在加拿大东部的北方森林中，土壤和叶面养分浓度和储量对氮沉降的增加具有潜在的弹性，因为在氮限制的情况下，额外的氮将被土壤微生物和植被迅速固定。这些发现可以改进未来北方森林土壤碳储量和生物量增长的建模，并有助于规划加拿大东部的森林管理战略。