Abstract The terrestrial carbon sink has increased since the turn of this century at a time of increased fossil fuel burning, yet the mechanisms enhancing this sink are not fully understood. Here we assess the hypothesis that regional increases in nitrogen deposition since the early 2000s has alleviated nitrogen limitation and worked in tandem with enhanced CO2 fertilization to increase ecosystem productivity and carbon sequestration, providing a causal link between the parallel increases in emissions and the global land carbon sink. We use the Community Land Model (CLM4.5‐BGC) to estimate the influence of changes in atmospheric CO2, nitrogen deposition, climate, and their interactions to changes in net primary production and net biome production. We focus on two periods, 1901–2016 and 1990–2016, to estimate changes in land carbon fluxes relative to historical and contemporary baselines, respectively. We find that over the historical period, nitrogen deposition (14%) and carbon‐nitrogen synergy (14%) were significant contributors to the current terrestrial carbon sink, suggesting that long‐term increases in nitrogen deposition led to a substantial increase in CO2 fertilization. However, relative to the contemporary baseline, changes in nitrogen deposition and carbon‐nitrogen synergy had no substantial contribution to the 21st century increase in global carbon uptake. Nonetheless, we find that increased nitrogen deposition in East Asia since the early 1990s contributed 50% to the overall increase in net biome production over this region, highlighting the importance of carbon‐nitrogen interactions. Therefore, potential large‐scale changes in nitrogen deposition could have a significant impact on terrestrial carbon cycling and future climate.

中文翻译：

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氮沉降和大气二氧化碳之间的协同作用是否推动了近期陆地碳汇的增强？

摘要 自本世纪之交以来，随着化石燃料燃烧的增加，陆地碳汇有所增加，但增强该碳汇的机制尚不完全清楚。在这里，我们评估了这样的假设：自 2000 年代初期以来，区域性氮沉降的增加缓解了氮限制，并与增加二氧化碳施肥协同作用，以提高生态系统生产力和碳固存，从而提供了排放量平行增加与全球土地碳之间的因果关系。下沉。我们使用社区土地模型 (CLM4.5-BGC) 来估计大气二氧化碳、氮沉降、气候变化的影响及其相互作用对净初级生产和净生物群落生产变化的影响。我们重点关注 1901-2016 年和 1990-2016 年这两个时期，分别估算相对于历史和当代基线的土地碳通量变化。我们发现，在历史时期，氮沉降（14％）和碳氮协同（14％）是当前陆地碳汇的显着贡献者，这表明氮沉降的长期增加导致二氧化碳施肥量大幅增加。然而，相对于当代基线，氮沉降和碳氮协同作用的变化对21世纪全球碳吸收的增加没有实质性贡献。尽管如此，我们发现自 20 世纪 90 年代初以来东亚氮沉降的增加对该地区生物群系净产量总体增长贡献了 50%，这凸显了碳氮相互作用的重要性。因此，氮沉积的潜在大规模变化可能对陆地碳循环和未来气候产生重大影响。