Forest ecosystems are important carbon (C) pools in terrestrial ecosystems, and the decomposition of soil organic matter depends on soil microbial metabolism. This study aimed to determine how forest thinning affects microbial metabolic limitation and microbial carbon use efficiency (CUE). We determined microbial metabolic limitations via extracellular enzymatic stoichiometry and microbial CUE by using a biogeochemical equilibrium model under different thinning intensities in the Qinling Mountains. We also analyzed the relationships among microbial metabolic processes and soil enzymes, soil properties (i.e., pH, soil nutrition content, and stoichiometry), and soil microbial biomass (i.e., microbial biomass and stoichiometry). Soil microbial metabolism was limited by C and phosphorus under the thinning intensities, and mild and moderate thinning intensities reduced the soil microbial C limitation. The effect of thinning intensity on CUE in the subsoil was greater than that in the topsoil. The pathways of CUE in the topsoil and subsoil differed, and microbial biomass and soil nutrients were the main factors affecting CUE in the topsoil and subsoil, respectively. Thinning changes the CUE by directly affecting microbial biomass in the topsoil, and thinning affects soil microbial biomass indirectly by affecting soil nutrients (i.e., total phosphorus), changing CUE in the subsoil. Our results show that moderate thinning can alleviate microbial metabolic limitation, and this finding has implications for understanding how microbial metabolism affects soil C dynamics under forest thinning.

中文翻译：

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间伐强度抑制秦岭天然次生林微生物代谢限制并提高微生物碳利用效率

森林生态系统是陆地生态系统重要的碳库，土壤有机质的分解取决于土壤微生物的代谢。本研究旨在确定森林间伐如何影响微生物代谢限制和微生物碳利用效率（CUE）。我们利用秦岭不同疏伐强度下的生物地球化学平衡模型，通过细胞外酶化学计量和微生物 CUE 确定了微生物代谢限制。我们还分析了微生物代谢过程与土壤酶、土壤性质（即pH、土壤营养含量和化学计量）以及土壤微生物生物量（即微生物生物量和化学计量）之间的关系。间伐强度下土壤微生物代谢受到C和磷的限制，轻度和中度间伐强度降低了土壤微生物C的限制。间伐强度对下层土CUE的影响大于表层土。表土和下土CUE的途径不同，微生物量和土壤养分分别是影响表土和下土CUE的主要因素。间伐通过直接影响表土中的微生物生物量来改变CUE，而间伐则通过影响土壤养分（即总磷）、改变底土中的CUE来间接影响土壤微生物生物量。我们的结果表明，适度间伐可以缓解微生物代谢限制，这一发现对于理解森林间伐下微生物代谢如何影响土壤碳动态具有重要意义。