<strong>Contrasting exogenous and endogenous soil microbial carbon use efficiencies under global changes</strong>

Microbial carbon use efficiency (CUE) is a critical parameter for controlling soil carbon dynamic. It is divided into microbial exogenous CUE (CUEex) and microbial endogenous CUE (CUEen) based on microbial utilization of carbon derived from organic material and soil organic matter. Global changes encompassing warming, dramatically decreased precipitation (drought) events, anthropogenic nutrient addition, and plant invasion can strongly influence microbial CUEex and CUEen. However, the responses of microbial CUE to global changes remain unclear, which can lead to significant uncertainties when forecasting terrestrial ecosystem carbon cycling under global changes. To address this issue, we analyzed 196 paired microbial CUEex and 97 paired microbial CUEen data and found that microbial CUEex decreased significantly with absolute latitude, while microbial CUEen showed the opposite trend. Warming had significant negative impacts on microbial CUEex and CUEen with decreases of 16.0% and 28.3%, respectively. Decreased precipitation had a mixed effect; increasing microbial CUEex by 7.9% but decreasing microbial CUEen by 14.4%. Nutrient addition had a consistently negative impact on microbial CUEex, decreasing it by 3.9-14.8%. The application of nitrogen, and nitrogen combined with phosphorus and potassium significantly increased microbial CUEen by 32.8% and 43.1%, respectively. Invasive plants significantly decreased microbial CUEex by 11.5%. Global change enhanced the microbial growth rate by 6.5%; however, when combined with added exogenous carbon there was a decrease of 3.2%. Aridity index, soil pH, and soil cation exchange capacity were the primary determinants of microbial CUEex in response to global changes. In contrast, microbial respiration and growth rates, followed by microbial biomass carbon, were found to be the most influential predictors of microbial CUEen. Therefore, it is essential to differentiate the magnitude, direction, and driving factors of microbial CUEex and CUEen in biogeochemical models, to accurately predict terrestrial ecosystem carbon cycling and potential feedbacks to global changes.微生物碳利用效率（Microbial carbon use efficiency, CUE）是调控土壤碳动态的关键参数。依据微生物对有机物料源碳与土壤有机质源碳的利用方式，可将其划分为外源微生物碳利用效率（microbial exogenous CUE, CUEex）与内源微生物碳利用效率（microbial endogenous CUE, CUEen）。全球变化因子涵盖增温、极端降水减少（干旱）事件、人为养分添加以及植物入侵，这些因素均可显著影响微生物CUEex与CUEen。但目前学界对微生物CUE响应全球变化的机制仍不明确，这会导致在预测全球变化背景下陆地生态系统碳循环时产生显著不确定性。为解决这一问题，本研究整合分析了196组配对的微生物CUEex数据与97组配对的微生物CUEen数据，结果显示：微生物CUEex随绝对纬度升高呈显著下降趋势，而微生物CUEen则呈现相反的变化规律。增温对微生物CUEex与CUEen均产生显著负向影响，分别使其降低16.0%与28.3%。降水减少的影响兼具双重性：可使微生物CUEex提升7.9%，却使微生物CUEen降低14.4%。养分添加对微生物CUEex始终表现为负向调控作用，使其降低3.9%~14.8%；而单独施用氮肥，以及氮肥配施磷钾肥则分别使微生物CUEen显著提升32.8%与43.1%。入侵植物可使微生物CUEex显著降低11.5%。全球变化整体使微生物生长速率提升6.5%，但当同时添加外源碳时，微生物生长速率则下降3.2%。干旱指数、土壤pH与土壤阳离子交换量是调控微生物CUEex响应全球变化的核心驱动因子；相较而言，微生物呼吸速率、微生物生长速率，随后是微生物生物量碳，是影响微生物CUEen的最关键预测因子。因此，在生物地球化学模型中，有必要区分微生物CUEex与CUEen的变化幅度、方向及驱动因子，从而精准预测陆地生态系统碳循环及其对全球变化的潜在反馈。