Effects of maize/soybean intercropping on rhizosphere soil phosphorus availability and functional genes involved in phosphorus cycling in Northwest China

Maize/soybean intercropping is a commonly employed agricultural technique with significant implications for enhancing crop productivity. However, the mechanisms by which rhizosphere soil microbial communities modulate genetic-level phosphorus (P) availability in maize/soybean intercropping systems in Northwest China remain unexplored. The effects of maize/soybean intercropping on rhizosphere soil P availability and P cycling-related genes were evaluated using the biologically based P fractionation method and metagenomics. Soil organic carbon, total P, available P, and P activation coefficient improved in the maize/soybean intercropping. Further, the content of soil P fractions followed the order HCl-P > citrate-P > enzyme-P > CaCl2-P. The dominant soil microbial phyla were Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, and Planctomycetes. The results of principal component analysis and nonmetric multidimensional scaling indicate that soil microbial composition differed among systems. The genes phoD, ppa, ppx, and pstC up-regulated in the intercropping, the results of random forest analysis indicate that these genes have the highest explanation for available P, suggesting that the improved P availability in the intercropping might be due to the up-regulation of these gene expressions. Redundant analysis indicated that pH and microbial biomass P significantly correlated with P fractions, suggesting they are essential factors in influencing P availability. Inorganic P solubilization, regulatory, and transporter genes were found to be associated with soil pH, total P, and alkaline phosphatase, suggesting they are the key factors that affect the expression of genes related to soil P cycling. Maize/soybean intercropping can increase rhizosphere soil P availability. While there are associations between available P and microbial genes, it is important to note that soil properties play a more pivotal role than genes in determining soil P availability.