[Research advances in soil microbial carbon use efficiency in response to climate change]

Soil microbial carbon use efficiency (CUE), defined as the proportion of assimilated carbon allocated to microbial growth versus maintenance, is a key parameter regulating terrestrial soil organic carbon (SOC) storage. The response of CUE to climate change and its feedbacks profoundly affect global carbon cycle and soil carbon sequestration. At present, there are substantial uncertainties regarding the mechanisms underlying the responses of CUE to climate change and the ecological consequences. We synthesized research progress on soil microbial CUE over the past 20 years. First, we clarified the basic concept and computational approaches of CUE, and compared the principles, strengths, and limitations of three mainstream measurement techniques (isotope labeling method, stoichiometric model, and thermodynamic efficiency method). Second, we summarized the key biotic and abiotic factors influencing CUE. Focused on the mechanisms underlying the main and interactive effects of elevated atmospheric CO₂ concentration, climate warming, and altered precipitation patterns on microbial CUE, and based on a "resource-cost trade-off" framework, we discussed the potential mechanisms underlying the heterogeneous responses of CUE across different ecosystems, and summarized the bottlenecks and challenges that still existed in current research regarding methodological standardization, the analysis of deep soil processes, the quantification of multi-factor interaction effects, and the application of CUE in earth system models (ESMs). We proposed an integrative research framework spanning from micro-scale metabolic mechanisms to macro-scale carbon cycling patterns, emphasizing the need for methodological innovation, multi-scale networked observations, and model-experiment integration, to thoroughly reveal the dynamics and adaptive mechanisms of CUE under climate change.