Metagenomic Insights into Microbial Functional Potential Associated with Soil Carbon, Nitrogen, and Phosphorus Cycling Along an Elevational Gradient in a Warm-Temperate Forest

Soil microbial functional potential is crucial to maintaining forest productivity and ecosystem functions. However, how microbially mediated soil nutrient cycling responds to environmental changes, particularly those caused by variations in elevation, remains poorly understood. Using the natural temperature gradient in a temperate mountain forest, this study investigated the differences in functional microbial groups and functional genes involved in soil carbon, nitrogen and phosphorus cycling along the elevation gradient, and analyzed the associations between environmental factors and these differences. The results showed that the low-elevation gradient (LE) had significantly higher abundances of genes involved in carbon degradation (pfkC, pgi1, and LSC1) but significantly lower abundances of those involved in carbon fixation (K18602, K18603, and K18604). Compared with the high-elevation gradient (HE), the LE had a significantly higher abundance of the nitrogen-cycle gene involved in organic degradation and synthesis (nao), but significantly lower abundances of denitrification (norB) and dissimilatory nitrate reduction genes (narG, narI, and napC). The abundances of the key genes involved in phosphorus metabolism (aphA and purO) were significantly higher at HE than at LE, whereas the abundance of the key gene associated with phosphorus transport (phnT) was significantly lower. The composition of the microbial community at the phylum level involved in carbon, nitrogen and phosphorus cycling at different elevations was similar, but the relative abundance of Thermoproteota and Nitrospirota increased significantly at HE. The annual average temperature, pH and carbon acquisition enzymes (β-glucosidase and β-D-cellobiosidase) were significantly associated with microbial community composition and functional genes related to carbon, nitrogen and phosphorus cycles. Additionally, genes involved in the carbon, nitrogen and phosphorus cycles were closely related through synergy and antagonism, especially the metabolic pathways encoded by purO, phnT and nrfA. These results provide metagenomic insights into the response patterns of microbial functional potential associated with soil carbon, nitrogen, and phosphorus cycling along an elevational gradient in a warm-temperate forest.