Determining which species to utilize for the artificial restoration of subtropical secondary forests has become a focal point in forestry and ecology. To compare the effects of the subtropical secondary forest artificial restoration model on soil microbial nutrient acquisition and limitation, we examined secondary forests (CKs), evergreen coniferous forests (GCPs), evergreen coniferous mixed broad-leaved forests (GCBMs), evergreen mixed broad-leaved forests (GBMs), and natural deciduous broad-leaved mixed forests (DBMs) as research subjects. Among them, GCPs, GCBMs, and GBMs were dominated by the species of the early, middle, and climax stages of subtropical forest succession, respectively. The activities and stoichiometry of β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP), and acid phosphatase (ACP) in the topsoil were analyzed. The results showed that the forest type significantly affects the activities of BG and LAP rather than NAG or ACP. The BG activity in DBMs was the lowest, while the LAP activity in CKs was significantly higher than that in plantations. Furthermore, the nutrient limitation of microbes was quantitatively analyzed by using the vector analysis of enzyme stoichiometry. The soil microbes in the study area were co-limited by C and P, and the nutrient limitation was in the order of C > P > N. Among the forests, the enzyme stoichiometric ratios in GCPs and DBMs were closest to 1:1:1. From CKs to GBMs, the microbial C limitation was increased, while the P limitation was decreased. The C limitation in DBMs was slightly lower than that in CKs. Overall, the P limitation in evergreen plantations was less than that in CKs. The soil bulk density, C/P, and N/P significantly influenced enzyme activities and stoichiometry. These results suggest that the artificial restoration of subtropical forests using evergreen species alleviated P limitation, while using deciduous broad-leaved species offered potential for alleviating microbial C limitation. Compared with evergreen broad-leaved species, employing pioneer and mid-successional or deciduous broad-leaved species can better achieve balanced microbial nutrient requirements.

Converting monoculture forests into mixed forests is a widely adopted strategy to enhance forest ecosystem quality. Soil enzyme activities and their stoichiometric ratios are acknowledged as critical indicators of nutrient cycling and ecosystem multifunctionality, with microbial nutrient limitation (particularly C, N, and P) being strongly influenced by forest management practices. However, the effects of this conversion on soil enzyme activities and stoichiometric ratios remain inconclusive, and the impacts of forest conversion on soil C, N, and P dynamics require further clarification. To address these uncertainties, a meta-analysis of 2113 paired observations was conducted to assess the impacts of forest conversion on soil enzyme activities, stoichiometric ratios, and microbial nutrient limitations. The activities of four key enzymes, including β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP), and phosphatase (ACP) were examined. It was found that mixed forests exhibited significantly higher C-, N-, and P- enzyme activities than monocultures (increases of 36.23%, 9.85%, and 11.07%, respectively). Additionally, soil C, N, and P contents were generally enhanced following the conversion from monocultures to mixed forests. Elevated enzyme C:P and N:P ratios were observed in mixed forests, while C:N ratios were reduced. Microbial C limitation was alleviated, though C&P co-limitation remained prevalent. Notably, greater effects on enzyme activities were observed when conifer monocultures (particularly those introduced with broadleaf species) were converted, compared with conversions of broadleaf monocultures. In contrast, the introduction of additional conifer species into existing conifer stands exacerbated C limitation. These results suggest that conversion of monocultures to mixed-species forests can mitigate microbial C limitation in soils while improving soil nutrient availability. Furthermore, for conifer plantation conversion, selecting functionally complementary broadleaf species yields greater benefits than introducing additional conifer species.