Decomposition of soil organic matter by microorganisms is a fundamental mechanism driving the terrestrial carbon (C) cycle. Microbial C use efficiency (CUE), microbial biomass residence time (MRT), and soil C temperature sensitivity (Q₁₀) co-determine the fate of soil C in a changing climate. In order to reveal the effect of soil depth and varying hydrologic properties on CUE, MRT, and Q₁₀ of microbial respiration, we incubated soils from three ecosystems (wetland, grassland, and forest) and soil depths (0–10, 20–30, and 50–60 cm) at two temperatures (10 and 30 °C). Microbial CUE was estimated using a substrate-independent method by incorporating ¹⁸O from labeled water into microbial DNA with the simultaneous measurement of microbial respiration. CUE ranged from about 0.2 to 0.7 with a mean value of 0.5 ± 0.1, MRT ranged from 4 to 73 days with a mean value of 26 ± 19 days, and Q₁₀ ranged from 1.8 to 2.9, averaging 2.3 ± 0.3 across all samples. We found that CUE increased but MRT and Q₁₀ decreased along the wetland-grassland-forest hydrologic gradient; and they all increased with soil depth. Moreover, CUE and MRT were lower at 30 °C than that at 10 °C. Although there were some differences in factors regulating the variation in CUE, MRT or Q₁₀ among soil depths and ecosystem types, both within individual ecosystems and depths, CUE, MRT, and Q₁₀ were strongly correlated to available C:N ratios, clay content, and C quality, respectively. In conclusion, our findings emphasize the importance of stoichiometry and C quality of available substrates in predicting the variation in microbial C use efficiency and soil C temperature sensitivity in different soil depths and along a hydrologic gradient.

微生物对土壤有机物的分解是驱动地球碳（C）循环的基本机制。微生物C的利用效率（CUE），微生物生物质的停留时间（MRT）和土壤C的温度敏感性（Q ₁₀）共同决定了气候变化下土壤C的命运。为了揭示土壤深度和不同的水文特性对微生物呼吸的CUE，MRT和Q ₁₀的影响，我们温育了三种生态系统（湿地，草地和森林）的土壤和土壤深度（0-10、20-30）和50–60 cm）在两个温度（10和30°C）下进行。微生物CUE的估算采用了与底物无关的方法，方法是将¹⁸O从标记的水变成微生物DNA，同时测量微生物的呼吸。CUE的范围约为0.2至0.7，平均值为0.5±0.1，MRT的范围为4至73天，平均值为26±19天，Q _10的范围为1.8至2.9，所有样本的平均值为2.3±0.3。我们发现，沿湿地-草地-森林水文梯度，CUE增加了，但MRT和Q ₁₀减少了；并且它们都随着土壤深度的增加而增加。此外，CUE和MRT在30°C时低于10°C。尽管在土壤深度和生态系统类型之间调节CUE，MRT或Q ₁₀变化的因素存在一些差异，但在各个生态系统和深度，CUE，MRT和Q中_10个分别与可用的C：N比，粘土含量和C品质密切相关。总之，我们的发现强调了化学计量和可用基质的碳质量在预测不同土壤深度和水文梯度中微生物碳利用效率和土壤碳温度敏感性变化方面的重要性。