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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. • Forest thinning altered microbial metabolic limitation. • Soil microbes were limited by the C and P under different thinning intensities. • Moderate thinning alleviated microbial metabolic limitation. • Forest thinning changed carbon use efficiency by affecting microbial biomass. [ABSTRACT FROM AUTHOR]

• Soil microbes were co-limited by the C and P during oak forest restoration, but these limitations tended to decrease gradually. • Rhizosphere soil microorganisms were subject to relatively strong C limitation and weak P limitation compared with those in bulk soil. • Microbial C and P limitation in the rhizosphere soil were mainly dependent on the DOC and Olsen−P. • An increase in the soil water content decreased the relative P limitation for the rhizosphere microbial community. Microbial metabolism changes in soil systems along a vegetation restoration gradient have attracted considerable attention; however, the differences in microbial metabolic limitations between the rhizosphere and bulk soil and their drivers during natural secondary forest restoration after disturbance have rarely been investigated. Here, we used multiple methods based on extracellular enzymatic stoichiometry to examine the microbial metabolic limitations in the rhizosphere and bulk soils along with a clear-cut oak (Quercus aliena var. acuteserrata) forest restoration over 58 years in the Qinling Mountains, China. Overall, the microbial metabolisms in both rhizosphere and bulk soils were co-limited by the availability of soil carbon (C) and phosphorus (P), and the limitations tended to decrease during restoration. Rhizosphere soil microorganisms were subject to relatively strong C limitation and weak P limitation compared with those in bulk soil. Microbial C and P limitations in the bulk soil were regulated by the nutrient ratios, and those in the rhizosphere soil were mainly dependent on the available nutrients mediated by soil moisture. Our results indicate that variations in the soil nutrients caused by oak forest restoration and water differences caused by the rhizosphere effect regulated microbial C and P metabolism in the rhizosphere and bulk soils. This study highlights the microbial metabolism difference between rhizosphere and bulk soil and its drivers during oak forest restoration and provides insights into the microbial resource limitation, nutrient cycling, and rhizosphere processes in the natural secondary forests after clear-cutting. [ABSTRACT FROM AUTHOR]