Ke-Qing Xiao, Chao Liang, Zimeng Wang, Jingjing Peng, Yao Zhao, Ming Zhang, Mingyu Zhao, Yong-Guan Zhu, Caroline Peacock

Microbial carbon use efficiency (CUE) is defined as the proportion of microbial biomass growth C versus substrate C uptake, and thus provides a useful measure of microbially driven accumulation and loss of soil organic carbon (SOC) 1. In a recent study published in Nature 2, the authors use a data-driven machine learning approach to conclude that CUE promotes global SOC storage based on a positive correlation between CUE and SOC content and that based on sensitivity analysis CUE is at least four times as important as six other evaluated factors, namely plant C inputs, C input allocation, non-microbial C transfer, substrate decomposability, environmental modifications and vertical transport. We agree with the authors that there is no consensus in the scientific community about the relationship between CUE and SOC, and that increasingly used big data methods offer an opportunity to synthesize and potentially generate new insights from multiple data aggregation. We argue however, that their study excludes important data sets and lacks mechanistic consideration of the complexities of SOC formation, such that their conclusions need to be clarified.