Soil metagenomics reveals distinct functional gene partitioning: Coniferous mixed stands vs. pure stands

China's large-scale cultivation of single artificial pure forests has led to soil degradation and a decline in microbial diversity, which has made managers pay more attention to the ecological benefits brought by mixed tree species. However, little is known about the differences in functional genes related to soil element cycling among different coniferous stand types. This study used metagenomic sequencing to examine the differences in functional genes related to carbon (C), nitrogen (N), and phosphorus (P) cycles in soil microbial communities among pure coniferous stands ( Cunninghamia lanceolata (Lamb.) Hook., CL; Pinus massoniana Lamb., PM) and mixed coniferous forest stand (CM) in southern Jiangsu hills. The results show that CM had higher soil nutrient contents compared to CL and PM, with a total C content of 31.8 g·kg −1 and total P content of 0.26 g·kg −1 , respectively. Meanwhile, the CM harbored more abundant microbial taxa and a more complex community structure, among which the bacterial Shannon and Richness indexes reached 4.7 and 12,700, respectively. Functional genes related to carbon fixation in the C cycle (e.g., cdhE , cdhD ), as well as those related to nitrate and nitrite reduction in the N cycle (e.g., narG , narH , nirS ), were more abundant in CM. In contrast, functional genes associated with the nitrogen cycle (e.g., norC , napA , nrfH ) and those linked to the phosphorus cycle (e.g., phnC , phnX , phnE ) exhibited higher abundances in CL and PM. The distribution of these functional genes was associated with microbial communities shaped by the soil environment: Acidobacteria and Proteobacteria were enriched in CL and PM, while Actinobacteria was a key microbial taxon in CM. Additionally, partial least squares path modeling identified soil physicochemical properties were strongly correlated with element cycles. In conclusion, our findings suggest that different coniferous stands provide unique potential benefits for soil health and ecosystem functions. These results advance our understanding of microbial roles in forest element cycles and offer novel insights into explaining the complex relationships among soil physical and chemical factors, microorganisms, and related functional genes.