Soil solution is the liquid phase of soil containing nutrients that are essential for vegetation’s health and growth. As such, soil solution chemistry is directly related to nutrient cycling and productivity in forest ecosystems. However, the long-term impacts of elevated N deposition on boreal forest soil solution composition remain uncertain. In this study, we investigate the effects of two decades of ammonium nitrate addition applied at rates of 3 (LN treatment) and 10 (HN treatment) times the ambient N deposition on soil solution collected weekly during the snow-free period at a black spruce boreal forest site located in eastern Canada. We show that N addition corresponding to 60 years (LN treatment) and 200 years (HN treatment) of accelerated ambient N deposition had nearly no important nor lasting impacts on soil solution NO₃⁻ and NH₄⁺ concentrations. This reveals that N deposition will most likely not significantly impact Canadian boreal forests soil solution inorganic N concentration in the future. Based on these results and along with NOx emissions data measured globally in North America and on NO₃–N deposition recorded at our experimental forest site, it is also likely that N deposition never affected Canadian forests’ soil chemistry in the past, even at the peak of N emission in North America in the 70 s. Our results indicate a surprisingly strong and widespread resilience of the eastern Canadian boreal forest soil solution chemistry and inorganic N content to long-term N deposition. This resilience can be partially explained by an important N-limitation in high-latitude forest ecosystems.

土壤溶液是土壤的液相，含有对植被健康和生长至关重要的养分。因此，土壤溶液化学与森林生态系统中的养分循环和生产力直接相关。然而，氮沉降升高对北方森林土壤溶液组成的长期影响仍不确定。在这项研究中，我们调查了在无雪期间每周在位于加拿大东部的黑云杉北方森林遗址以环境氮沉积的 3 倍（LN 处理）和 10 倍（HN 处理）对土壤溶液进行二十年硝酸铵添加的影响。我们表明，对应于 60 年 （LN 处理） 和 200 年 （HN 处理） 加速环境 N 沉积的 N 添加对土壤溶液 NO₃^- 和 NH₄⁺ 浓度几乎没有重要或持久的影响。这表明 N 沉降在未来很可能不会显着影响加拿大北方森林土壤溶液无机 N 浓度。根据这些结果，以及在北美全球测量的 NOx 排放数据以及我们实验林场记录的 NO_3-N 沉积，氮沉积很可能过去从未影响过加拿大森林的土壤化学，即使在 70 年代北美氮排放的高峰期也是如此。我们的结果表明，加拿大东部北方森林土壤溶液化学和无机氮含量对长期氮沉积具有令人惊讶的强大和广泛的恢复力。这种恢复力可以部分解释为高纬度森林生态系统中的一个重要 N 限制。