Sensitivity of global soil carbon stocks to combined nutrient enrichment

Soil stores approximately twice as much carbon as the atmosphere and fluctuations in the size of the soil carbon pool directly influence climate conditions. We used the Nutrient Network global change experiment to examine how anthropogenic nutrient enrichment might influence grassland soil carbon storage at a global scale. In isolation, enrichment of nitrogen and phosphorous had minimal impacts on soil carbon storage. However, when these nutrients were added in combination with potassium and micronutrients, soil carbon stocks changed considerably, with an average increase of 0.04 KgCm−2 year−1 (standard deviation 0.18 KgCm−2 year−1). These effects did not correlate with changes in primary productivity, suggesting that soil carbon decomposition may have been restricted. Although nutrient enrichment caused soil carbon gains most dry, sandy regions, considerable absolute losses of soil carbon may occur in high‐latitude regions that store the majority of the world's soil carbon. These mechanistic insights into the sensitivity of grassland carbon stocks to nutrient enrichment can facilitate biochemical modelling efforts to project carbon cycling under future climate scenarios.

土壤碳储量约为大气碳储量的两倍，土壤碳库（soil carbon pool）规模的波动会直接影响气候状况。本研究依托养分网络（Nutrient Network）全球变化实验平台，在全球尺度下探究人为养分富集对草原土壤碳储量的影响。单独施加氮、磷养分时，其对土壤碳储量的影响极微；但当将这些养分与钾及微量营养素配施时，土壤碳储量会发生显著变化，平均增幅达0.04千克碳每平方米每年（kg C m⁻² yr⁻¹），标准偏差为0.18千克碳每平方米每年。该效应与植物初级生产力的变化并无关联，这表明土壤碳分解过程可能受到了抑制。尽管养分富集在多数干旱沙质区域带来了土壤碳储量的增加，但在储存了全球绝大多数土壤碳的高纬度地区，土壤碳储量可能会出现显著的绝对损失。上述关于草原碳储量对养分富集响应机制的深入认识，可为未来气候情景下碳循环预测的生物化学建模工作提供有力支撑。