Soils store more carbon than other terrestrial ecosystems^1,2. How soil organic carbon (SOC) forms and persists remains uncertain^1,3, which makes it challenging to understand how it will respond to climatic change^3,4. It has been suggested that soil microorganisms play an important role in SOC formation, preservation and loss^5,6,7. Although microorganisms affect the accumulation and loss of soil organic matter through many pathways^{4,6,8,9,10,11}, microbial carbon use efficiency (CUE) is an integrative metric that can capture the balance of these processes^12,13. Although CUE has the potential to act as a predictor of variation in SOC storage, the role of CUE in SOC persistence remains unresolved^7,14,15. Here we examine the relationship between CUE and the preservation of SOC, and interactions with climate, vegetation and edaphic properties, using a combination of global-scale datasets, a microbial-process explicit model, data assimilation, deep learning and meta-analysis. We find that CUE is at least four times as important as other evaluated factors, such as carbon input, decomposition or vertical transport, in determining SOC storage and its spatial variation across the globe. In addition, CUE shows a positive correlation with SOC content. Our findings point to microbial CUE as a major determinant of global SOC storage. Understanding the microbial processes underlying CUE and their environmental dependence may help the prediction of SOC feedback to a changing climate.

土壤比其他陆地生态系统储存更多的碳^1,2 。土壤有机碳 (SOC) 如何形成和持续存在仍不确定^1,3 ，这使得了解其如何应对气候变化变得具有挑战性^3,4 。有人认为，土壤微生物在 SOC 的形成、保存和损失中发挥着重要作用^5,6,7 。尽管微生物通过多种途径影响土壤有机质的积累和损失^{4,6,8,9,10,11} ，但微生物碳利用效率（CUE）是一个综合指标，可以捕捉这些过程的平衡^12,13 。尽管 CUE 有潜力作为 SOC 存储变化的预测因子，但 CUE 在 SOC 持久性中的作用仍未得到解决^7,14,15 。在这里，我们结合全球规模数据集、微生物过程显式模型、数据同化、深度学习和荟萃分析，研究了 CUE 与 SOC 保护之间的关系，以及与气候、植被和土壤特性的相互作用。我们发现，在确定 SOC 存储及其在全球范围内的空间变化时，CUE 的重要性至少是其他评估因素（例如碳输入、分解或垂直运输）的四倍。此外，CUE与SOC含量呈正相关。我们的研究结果表明微生物 CUE 是全球 SOC 存储的主要决定因素。了解 CUE 背后的微生物过程及其环境依赖性可能有助于预测 SOC 对气候变化的反馈。