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

Abstract

Purpose Maize/soybean intercropping is widely used as a vital practice to improve crop yields in northwest China. However, it is unknown how rhizosphere soil microbes regulate the P availability at the genetic level in maize/soybean intercropping. Methods We conducted an experiment to evaluate the effect of maize/soybean intercropping on rhizosphere soil P availability and P cycling functional genes using the BBP fractions and metagenomics methods. Soil samples were collected in the M, S, IM and IS. Results The SOC, TP, AP and PAC are improved in IM and IS. P fractions followed the order HCl-P > Citrate-P > Enzyme-P > CaCl2-P. The dominate soil microbial phyla were Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi and Planctomycetes. PCA and NMDS indicated that soil microbial composition differed among treatments. The abundance of phoD, ppa, ppx and pstC upregulated in the IM, the random forest analysis showed that these genes have the highest explanation for AP, suggesting that the improved availability in IM may due to the upregulation of these genes. RDA analysis indicated that pH, SMBP significantly correlated with P fractions, indicating that pH and SMBP are important factors in influencing soil P bioavailability. Inorganic P solubilization, regulatory and transporter genes were correlated with soil pH, TP and ALP, suggesting they were the key factors affecting the expression of functional genes related to soil P cycling. Conclusion Maize/soybean intercropping can increase rhizosphere soil P bioavailability. Although there are relationships between soil AP and microbial genes (phoD, ppa, ppx,and pstC), soil properties are more crucial than genes in shaping soil P bioavailability.