Aims Under the background of changing carbon cycle process in forest ecosystems caused by global environmental change, the microbial carbon use efficiency（CUE） in forest rhizosphere soil is critical to determine the strength of microbial anabolism and catabolism in forest ecosystems. However, the variation and influencing factors of microbial CUE in rhizosphere soils at different altitudes remain undetermined.Methods Rhizosphere soil at six different altitudes spanning four forest belts in Taibai Mountain was sampled to determine the physical and chemical properties, extracellular enzyme activity, and characteristics of microbial community and vegetation. Based on the stoichiometric ratio, the soil microbial CUE was estimated. Furthermore,the variation in microbial CUE of rhizosphere soil along the altitude gradient was analyzed to quantify the influencing factors of microbial CUE.Important findings The results showed that the microbial CUE of rhizosphere soil exhibited an overall upward trend with the increase in altitude. The microbial CUE increased by 4.36% from 0.505 at the lowest altitude to 0.527 at the highest altitude, but decreased at 1 603 and 2 405 m. Based on the Mantel analysis, we identified four categories of factors（i.e., altitude, soil matrix, vegetation and microbe） that related to microbial CUE in rhizosphere soil. The variations of microbial CUE in rhizosphere soil are affected by multiple environmental factors, with the dominant factor being soil matrix（such as dissolved organic carbon（DOC） content, ammonium nitrogen（NH 4 + -N） content）, followed by vegetation. Furthermore, the altitude factor and the microbial factor explained 2.6% and 3.1% of the CUE change, respectively. Although the microbial factors exerted no significant impact on microbial CUE, soil matrix, vegetation and microbe jointly explained 47.0% of the microbial CUE change. The variance partitioning analysis（VPA） quantitatively revealed the contribution of environmental factors to the change of microbial CUE, where soil matrix and vegetation explained 17.0% and 5.7% of the variation, respectively. While the interaction between soil matrix and vegetation accounted for 31.9% of the changes in microbial CUE. The above results indicated that the high-altitude rhizosphere soil in Taibai Mountain has a high carbon sequestration potential, and the carbon sequestration of forest rhizosphere soil may decrease with the intensification of global warming. The vertical temperature difference and the vertical differentiation of the vegetation belt induced by altitude gradient will alter the growth and metabolism environment of microorganisms in the rhizosphere soil. The comprehensive effect of multiple environmental factors dominated by soil matrix impacts the CUE of soil microorganisms, and ultimately changes the assimilation and catabolism processes of soil carbon. The results of this study can provide a scientific basis for the carbon assimilation capacity and carbon sequestration potential of forest soil microorganisms in Qinling Mountains, as well as the forest soil carbon cycle under the background of global change.

森林土壤碳库对全球变暖的响应是气候变暖下预测CO2不确定性的潜在主要来源.然而,不同植被带上各粒径团聚体的SOC矿化的温度敏感性(Q10)及机理尚不明确.收集了中国太白山4个不同海拔的植被带的土壤,将土壤按粒径大小筛分为大、中、小3类团聚体,并进行了100天的土壤培养实验,以监测在3个恒定温度(5℃、15℃和25℃)下土壤呼吸速率、微生物量碳和胞外酶活性等指标.研究表明(1)团聚体占全土比例随粒径增大而增大,而有机碳含量随粒径的增大而减小.(2)随着海拔的升高,大团聚体、中团聚体、小团聚体的惰性碳库比例分别从45.11％、36.37％、64.72％升高到45.71％、38.11％、67.12％,缓效碳库比例分别从28.81％、37.20％、14.54％下降到28.41％、36.16％、13.78％,活性碳库比例从26.06％、26.42％、20.73％下降到25.35％、25.72％、19.09％.(3)各团聚体温度敏感性(Q10)表现出随海拔升高而增加,随温度升高而降低(T1Q10＞T2Q10),并且具有惰性碳库Q10＞缓效碳库Q10＞活性碳库Q10的规律.(4)团聚体的微生物量碳(MBC)随着培养时间,各海拔、各温度下均呈现先升高后下降的趋势.(5)影响碳库和Q10的环境因素包括植被类型、土壤特性、土壤环境、土壤底物,其中植被表现较其他更强.