State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, China.
University of Chinese Academy of Sciences, Beijing, China.
Ecol Lett. 2022 Jan;25(1):77-88. doi: 10.1111/ele.13906. Epub 2021 Oct 25.
Nitrogen (N) deposition is known to increase carbon (C) sequestration in N-limited boreal forests. However, the long-term effects of N deposition on ecosystem carbon fluxes have been rarely investigated in old-growth boreal forests. Here we show that decade-long experimental N additions significantly stimulated net primary production (NPP) but the effect decreased with increasing N loads. The effect on soil heterotrophic respiration (Rh) shifted from a stimulation at low-level N additions to an inhibition at higher levels of N additions. Consequently, low-level N additions resulted in a neutral effect on net ecosystem productivity (NEP), due to a comparable stimulating effect on NPP and Rh, while NEP was increased by high-level N additions. Moreover, we found nonlinear temporal responses of NPP, Rh and NEP to low-level N additions. Our findings imply that actual N deposition in boreal forests likely exerts a minor contribution to their soil C storage.
氮（N）沉积已知会增加 N 限制的北方森林中的碳（C）固存。然而，在北方原始森林中，对 N 沉积对生态系统碳通量的长期影响的研究却很少。在这里，我们表明，长达十年的实验性 N 添加显著刺激了净初级生产力（NPP），但随着 N 负荷的增加，这种影响会减弱。对土壤异养呼吸（Rh）的影响从低水平 N 添加的刺激转变为高水平 N 添加的抑制。因此，由于对 NPP 和 Rh 具有可比的刺激作用，低水平 N 添加对净生态系统生产力（NEP）的影响呈中性，而高水平 N 添加则增加了 NEP。此外，我们发现 NPP、Rh 和 NEP 对低水平 N 添加的时间响应是非线性的。我们的研究结果表明，北方森林中实际的 N 沉积可能对其土壤 C 储存的贡献较小。
