Metagenomics reveals afforestation-driven shifts in microbial nitrogen and phosphorus cycling strategies in China's arid and semi-arid regions

Vegetation restoration in arid and semi-arid ecosystems can promote soil nutrient accumulation through the “fertile island effect”, yet microbial nitrogen (N) and phosphorus (P) cycling responses to afforestation remain poorly understood. In this study, metagenomic sequencing was used to investigate the functional potential of soil microbial N and P cycling in afforested and adjacent paired bare sandy land soils across 13 sites in arid region northwestern China. Our results demonstrate that afforestation significantly altered soil microbial community composition and was associated with higher TPM-normalized relative representation of genes involved in several N-cycling modules, including N mineralization, N fixation, nitrification, DNRA and N assimilation, as well as genes associated with P uptake and transport, inorganic P solubilization and P starvation response. Functional modules and associated genes showed distinct relationships with environmental and spatial variation. Analysis of the key module functional variation revealed that the DNRA was associated with soil nutrient conditions, while nrfA and nrfH differed in relative representation between afforested and paired bare soils. Similarly, variation in genes associated with organic P mineralization was related to edaphic conditions, accompanied by differences in the relative representation of phosphatase gene phoA and the C-P lyase gene cluster phn . Overall, afforestation was associated with shifts in relative N- and P-cycling functional gene profiles and microbial community composition. These findings provide a functional-genomic perspective for evaluating the ecological consequences of afforestation in arid and semi-arid ecosystems, and provide a scientific basis for evaluating afforestation effectiveness and guiding sustainable ecosystem restoration.