In the Northern Hemisphere, anthropogenic nitrogen (N) deposition contributed to the enhancement of the global terrestrial carbon (C) sink, partially offsetting CO2 emissions. Across several long‐term field experiments, this ecosystem‐level response was determined to be driven, in part, by the suppression of microbial activity associated with the breakdown of soil organic matter. However, since the implementation of emission abatement policies in the 1970s, atmospheric N deposition has declined globally, and the consequences of this decline are unknown. Here, we assessed the response of soil C storage and associated microbial activities, in a long‐term field study that experimentally increased N deposition for 24 years. We measured soil C and N, microbial activity, and compared effect sizes of soil C in response to, and in recovery from, the N deposition treatment across the history of our experiment (1994–2022). Our results demonstrate that the accumulated C in the organic horizon has been lost and exhibits additional deficits 5 years post‐termination of the N deposition treatment. These findings, in part, arise from mechanistic changes in microbial activity. Soil C in the mineral soil was less responsive thus far in recovery. If these organic horizon C dynamics are similar in other temperate forests, the Northern Hemisphere C sink will be reduced and climate warming will be enhanced.

中文翻译：

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人为氮沉降后土壤碳储量的增加在停止后迅速丧失


在北半球，人为氮 （N） 沉积有助于增强全球陆地碳 （C） 汇，部分抵消了 CO2 排放。在几次长期的田间实验中，确定这种生态系统水平的反应部分是由抑制与土壤有机质分解相关的微生物活动驱动的。然而，自 1970 年代实施减排政策以来，全球大气氮沉降量有所下降，这种下降的后果尚不清楚。在这里，我们在一项长期田间研究中评估了土壤 C 储存和相关微生物活动的反应，该研究通过实验增加了 24 年的 N 沉积。我们测量了土壤 C 和 N、微生物活性，并比较了土壤 C 在我们的实验历史 （1994-2022） 中响应 N 沉积处理和从中恢复的效应大小。我们的结果表明，有机层中积累的 C 已经丢失，并在 N 沉积处理终止 5 年后表现出额外的缺陷。这些发现部分源于微生物活性的机制变化。到目前为止，矿物土壤中的土壤 C 在恢复中的响应性较差。如果这些有机水平 C 动态在其他温带森林中相似，则北半球 C 汇将减少，气候变暖将加剧。