We are far from understanding the spatial patterns of dryland soil carbon and nitrogen stocks and how they vary among different land cover types. We used data from 12,000 sites from 129 countries in global drylands to estimate soil organic carbon (SOC) and total nitrogen (STN) stocks in different land cover types, explore the factors driving their spatial distribution, and predict the trends under different climate scenarios in global drylands. SOC and STN stocks in the upper 100 cm reached 419.5 and 38.2 Pg, respectively, with the upper 0–30 cm accounting for half of them. The largest SOC stocks were found in forests, shrublands and grasslands, while STN stocks peaked in forests, bare areas and croplands. The factors driving the spatial patterns of SOC and STN varied among soil depths, with mean annual temperature, pH and aridity being the main factors driving the spatial patterns in SOC and STN density for 0–30 cm, and soil texture the strongest factor for 60–100 cm. Under the Representative Concentration Pathways (RCP) 4.5 scenario, SOC and STN stocks were predicted to decrease by 3.6 % and 4.0 %, respectively, from 2020 to 2100, whereas under the RCP 8.5 scenario, the projected decreases were 5.9 % and 6.4 % respectively. Our results indicate that if we want to accurately predict C and N accumulation, and design effective mitigation measures in terrestrial ecosystems under future climatic scenarios, we need to better explore the drivers that operate at the deeper soil depths, which also accumulate a significant amount of SOC and STN.

中文翻译：

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全球旱地土壤碳氮积累的环境驱动因素


我们远未了解旱地土壤碳和氮储量的空间模式以及它们在不同土地覆盖类型之间如何变化。我们使用了来自全球干旱地区 129 个国家的 12,000 个站点的数据来估计不同土地覆盖类型的土壤有机碳 （SOC） 和总氮 （STN） 储量，探索驱动其空间分布的因素，并预测全球干旱地区不同气候情景下的趋势。上部 100 cm 的 SOC 和 STN 储量分别达到 419.5 和 38.2 pg，其中上部 0–30 cm 占一半。最大的土壤有机碳储量出现在森林、灌木丛和草原中，而 STN 储量在森林、裸露地区和农田中达到峰值。驱动土壤有机碳和土壤生长强度空间格局的因素因土壤深度而异，年均温度、pH和干旱度是驱动土壤有机碳和土壤生长强度密度空间格局的主要因素，60−100 cm土壤质地是影响土壤有机碳和土壤生长密度空间格局的主要因素。在代表性集中途径 （RCP） 4.5 情景下，预计从 2020 年到 2100 年，SOC 和 STN 库存将分别减少 3.6% 和 4.0%，而在 RCP 8.5 情景下，预计下降分别为 5.9% 和 6.4%。我们的结果表明，如果我们想准确预测 C 和 N 积累，并在未来气候情景下设计有效的陆地生态系统缓解措施，我们需要更好地探索在更深土壤深度起作用的驱动因素，这些驱动因素也积累了大量的 SOC 和 STN。