Vegetation restoration can regulate soil microbial habitat and carbon supply by altering soil physicochemical properties. However, it remains unclear how different vegetation restoration patterns influence soil microbial carbon cycling functions through these changes. This study investigated four vegetation restoration models including two coniferous forests —Platycladus orientalis (L.) Franco. (Cupressaceae, PO) and Pinus densiflora Siebold and Zucc. (Pinaceae, PS); one broadleaf forest—Quercus acutissima Carruth. (Fagaceae, QA); and a shrub (SH), using wasteland (WL) as a control. This study employed metagenomic sequencing technology in conjunction with analysis based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The research examined alterations in soil physicochemical characteristics, microbial community structure, and functional pathway associated with carbohydrate metabolism, carbon fixation, and methane metabolism. Vegetation restoration patterns had a strong impact on soil characteristics and microbial composition. Compared to WL, the PO treatment exhibited significant increases in soil organic carbon (SOC, 110.71%), phosphorus (TP, 400%), and bulk density (BD, 22.4%). Significant differences were observed in soil carbon cycle functional pathways, with overall abundance following the trend PO > WL > SH > PS > QA. The relative abundance of carbon fixation, methane metabolism, and carbohydrate metabolism pathways was highest in PO, significantly higher than in QA. Mantel test showed soil phosphorus, pH, and C; N strongly linked to microbial carbon cycling pathways, marking them as key regulators. We found that PO showed the highest abundance of carbon-cycling-related functional pathways, whereas PS showed a comparatively weaker response, suggesting species-specific variation rather than a uniform coniferous–broadleaf pattern. Vegetation restoration controls microbial carbon cycling through soil properties, especially phosphorus, pH, and nutrient balances. This knowledge supports better restoration planning for ecosystem carbon management.

The continuous monoculture in Populus × euramericana ‘Neva’ plantations is closely related to the accumulation of phenolic acids in the soil, and these phenolic compounds exert a certain influence on plant nitrogen uptake. Leguminous plants can replenish soil nitrogen through biological nitrogen fixation, which is of great significance for enhancing plant productivity. This study employed different concentrations of phenolic acid treatments (0T, 0.5T, 1.0T, 1.5T, 2.0T) to analyze the photosynthetic characteristics of five phenolic compounds in a poplar–soybean (Glycine max (L.) Merr.) intercropping system, thereby providing a basis for biological management strategies aimed at increasing the yield of poplar monoculture stands. The results indicate that (1) P_n in poplar monoculture, soybean monoculture, and soybean intercropping all decreased as phenolic acid concentration increased, whereas P_n in poplar intercropping increased with rising phenolic acid concentration. Under treatments ranging from 0T to 1.5T, the decrease in P_n in the pure poplar, pure soybean, and intercropped soybean systems was primarily due to stomatal limitations, whereas under treatments ranging from 1.5T to 2.0T, it was primarily due to non-stomatal limitations. (2) Poplar, soybean, and soybean-intercropped poplar adapted to environmental stress by dissipating excess light energy absorbed by PS II as heat. The intercropping system effectively optimized poplar fluorescence parameters and mitigated the damage caused by phenolic acid stress to its photosynthetic machinery. (3) Chlorophyll A, chlorophyll B, and total chlorophyll in poplar and soybean leaves were significantly inhibited. (4) The biomass of poplars grown in monoculture decreased as phenolic acid concentration increased, whereas the biomass of poplars in intercropping showed the opposite trend. It is evident that, under phenolic acid conditions, poplar–soybean intercropping can mitigate the effects of phenolic acid stress to a certain extent.