Changes of microbial life history strategies to soil nutrient limitations following vegetation restoration and its impact on carbon utilization efficiency.

Vegetation restoration often leads to changes in soil nutrients, prompting adjustments in microbial growth strategies and compositions. However, how microbial adaptive strategies affect microbial carbon use efficiency (CUE) remains unclear. This study utilized the space-for-time substitution method and involved three forest types in the Taiyi Mountain area as research objects for vegetation restoration: Platycladus orientalis (L.) Franco. (PO), Pinus densiflora Siebold & Zucc. (PS), and Quercus acutissima Carruth. (QA), with shrub (CT) serving as the control. Nutrient limitation changes and microbial adaptation strategies following vegetation restoration were quantified, and microbial CUE was calculated using biogeochemical stoichiometric models to explore how microbial adaptation strategies in response to nutrient limitation changes affect CUE following vegetation restoration. The results revealed that the activities of microbial carbon, nitrogen, and phosphorus cycle enzymes increased to different degrees following vegetation restoration compared with those in the control. Among these, the phosphorus cycle enzyme (ACP) activity in PO and PS increased most significantly, by 26.9 % and 16.8 %, respectively. Following vegetation restoration, compared with CT, the microbial biomass carbon (MBC) of PO increased significantly, from 171.80 μg/g to 382.51μg/g, and the microbial biomass nitrogen (MBN) of PO also increased significantly, from 19.63 μg/g to 34.91 μg/g. The microbial biomass phosphorus (MBP) decreased significantly, from 11.89 μg/g to 5.52 μg/g. Soil nitrogen limitation was enhanced and shifted from N to P limitation following vegetation restoration. To cope with these limitations, the soil microbial community Chao1 and Shannon decreased significantly, whereas the relative abundance of fungal K-strategy microorganisms increased, indicating a shift in the microbial life history strategy from the r-strategy to the K-strategy. The CUE ranged from 0.39 to 0.49 and significantly increased by 2.5 %, 1.9 %, and 2.4 % for PO, PS, and QA, respectively, following vegetation restoration. Partial least squares modeling (PLS-PM) provided further evidence that moderate nutrient limitation can increase CUE in coniferous forests by altering microbial adaptive strategies. Vegetation restoration induced soil P limitation promotes K-strategy microbes and higher CUE in coniferous forests, potentially making them superior to broadleaf forests for soil carbon sequestration.