Microbial carbon use efficiency (CUE) describes the partitioning of carbon (C) between respiration and growth, and this defines the soil-atmosphere C balance. Despite its importance, CUE is not properly represented in soil biogeochemical models. Here, we estimated how CUE varied in soil along a continental gradient. Through a structural equation model, we found that bacterial growth, fungal community composition, and SOM quality were the main drivers of CUE variation. Biotic factors controlled CUE directly, while soil properties and climate indirectly controlled CUE via biotic factors. Surprisingly, we found that microbial assimilability of SOM had a negative relationship with CUE. High rates of microbial SOM-use coincided with a greater growth-fraction used for respiration suggesting decoupled catabolism and anabolism, probably due to nutrient limitation. Our study highlights the importance of the microbial community composition to predict CUE and that interactions between bacterial and fungal communities can have implications for CUE.

中文翻译：

---

沿欧洲纬度梯度控制微生物碳利用效率

微生物碳利用效率（CUE）描述了碳（C）在呼吸和生长之间的分配，这定义了土壤-大气碳平衡。尽管 CUE 很重要，但它在土壤生物地球化学模型中并未得到适当的体现。在这里，我们估计了土壤中 CUE 如何沿着大陆梯度变化。通过结构方程模型，我们发现细菌生长、真菌群落组成和 SOM 质量是 CUE 变化的主要驱动因素。生物因素直接控制CUE，而土壤性质和气候通过生物因素间接控制CUE。令人惊讶的是，我们发现SOM的微生物同化性与CUE呈负相关。微生物 SOM 使用率较高，同时用于呼吸的生长分数较高，这表明分解代谢和合成代谢脱钩，这可能是由于营养限制所致。我们的研究强调了微生物群落组成对于预测 CUE 的重要性，以及细菌和真菌群落之间的相互作用可能对 CUE 产生影响。