Deciphering the linkage between ecological stoichiometry and ecosystem functioning under anthropogenic nitrogen (N) deposition is critical for understanding the impact of afforestation on terrestrial carbon (C) sequestration. However, the specific changes in above‐ versus belowground stoichiometric asymmetry with stand age in response to long‐term N addition remain poorly understood. In this study, we investigated changes in stoichiometry following a decadal addition of three levels of N (control, no N addition; low N addition, 20 kg N ha−1 year−1; high N addition, 50 kg N ha−1 year−1) in young, intermediate, and mature stands in three temperate larch plantations (Larix principis‐rupprechtii) in North China. We found that low N addition had no impact on both above‐ (leaf and litter) and belowground (soil and microbe) stoichiometry. In contrast, high N addition resulted in significant asymmetry in above‐ versus belowground stoichiometry, which then diminished during stand development. Following 10 years of N inputs, the young and intermediate plantations transitioned from a state of relative N limitation to co‐limitation by both N and phosphorus (P), whereas the mature plantation continued to experience relative N limitation. Conversely, soil microorganisms exhibited relative P limitation in all three plantations. Broader niche differentiation (N limitation for trees, but P limitation for microorganisms) under long‐term N input may have been responsible for the faster attainment of stoichiometric homeostasis in mature plantations than in young plantations. Our findings provide stoichiometric‐based insight into the operating mechanisms of large C sinks in young forests, particularly above‐ versus belowground C stock asymmetry, and highlight the need to consider the role of flexible stoichiometry when forecasting future forest C sinks.

中文翻译：

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在林分发育过程中，减弱地上和地下化学计量对年代际氮添加的不对称性


破译人为氮 （N） 沉积下生态化学计量与生态系统功能之间的联系，对于理解植树造林对陆地碳 （C） 封存的影响至关重要。然而，响应长期 N 添加的地上与地下化学计量不对称性随林龄的具体变化仍然知之甚少。在这项研究中，我们研究了华北三个温带落叶松人工林 （Larix principis‐rupprechtii） 的幼龄、中级和成熟林分在十年添加三个水平氮（对照，无氮添加;低氮添加，20 kg N ha-1 年-1;高氮添加，50 kg N ha-1 年-1）后化学计量的变化华北落叶松人工林。我们发现低 N 添加对地上（叶子和凋落物）和地下（土壤和微生物）化学计量没有影响。相比之下，高氮添加导致地上和地下化学计量的显著不对称性，然后在林分发育过程中减少。经过 10 年的氮输入，年轻和中间人工林从相对氮限制状态转变为氮和磷 （P） 的共同限制状态，而成熟人工林继续经历相对氮限制。相反，土壤微生物在所有 3 个人工林中都表现出相对的 P 限制。在长期 N 输入下，更广泛的生态位分化（树木的 N 限制，但微生物的 P 限制）可能是成熟人工林比年轻人工林更快地实现化学计量稳态的原因。 我们的研究结果为幼龄林中大型 C 汇的运行机制提供了基于化学计量学的见解，特别是地上和地下 C 储量的不对称性，并强调了在预测未来森林 C 汇时需要考虑灵活化学计量的作用。