Effects of different land use on functional genes of soil microbial carbon and phosphorus cycles in the desert steppe zone of the Loess Plateau.

Desert grassland ecosystems on China's Loess Plateau are characterized by diverse land use types and varying human disturbances. We aimed to evaluate how land use influences soil microbial communities and functional genes related to carbon (C) and phosphorus (P) cycling. To do this, we selected five representative land use types: natural grassland, 20-year abandoned farmland, 12-year alfalfa grassland, 5-year Lanzhou lily farmland, and 17-year Platycladus orientalis forest. High-throughput metagenomic sequencing and soil physicochemical analyses were conducted. Proteobacteria dominated the nutrient-rich lily soil, while Actinobacteria were more abundant in the other soils. Available phosphorus (AP) had the strongest influence on microbial community structure and gene composition (p < 0.01). The relative abundance of ppdK, rpiB, glpX, and epi (C fixation genes), and purS (purine metabolism) was significantly higher in forest soil than in abandoned farmland (p < 0.05). Similarly, forest soil showed elevated levels of mttB and acs (methanogenesis), sdhA (TCA cycle), pstS (P transport), and pps (pyruvate metabolism) compared to alfalfa soil. Lily soil exhibited significantly higher abundance of acr genes (involved in the hydroxypropionate-hydroxybutylate cycle) and phnE (an ATP-binding cassette transporter) than natural grassland and alfalfa soils (p < 0.05). Microbial networks involved in C and P cycling were simpler but more functionally specialized in forest soil. Positive microbial interactions related to C and P cycling were strongest in lily soil. These findings provide important insights into soil microbial functional adaptation and offer a foundation for sustainable land use management on the Loess Plateau.