Cotton-maize intercropping increases rhizosphere soil phosphorus bioavailability by regulating key phosphorus cycling genes in northwest China

Intercropping is widely used as an important means to promote crop productivity; but the underpinning mechanisms of rhizosphere soil microbial processes in shaping soil phosphorus (P) bioavailability under cotton-based intercropping systems have not been investigated in arid northwest China. Therefore, taking cotton-maize intercropping as an example, biologically based P (BBP) and metagenomics methods were used to investigate changes of soil P bioavailability, microbial community and functional P-cycling genes in the rhizosphere. Three treatments were cotton monoculture, maize monoculture and cotton-maize intercropping. We found that rhizosphere soils from cotton-maize intercropping exhibited higher soil organic matter (SOM), available P (AP), and alkaline phosphatase (ALP) than those of crop monocultures ( p < 0.05). The change of bioavailable-P fractions in the order HCl-P > Citrate-P > Enzyme-P > CaCl 2 -P, and higher mount of CaCl 2 -P, Citrate-P and Enzyme-P were observed in soil samples from cotton-maize intercropping. These results indicated that P bioavailability were improved after two crops intercropping. The dominate soil microbial community from all treatments belonged to the phyla Proteobacteria , Actinobacteria , Acidobacteria , Chloroflexi and Gemmatimonadetes . In addition, we observed that the expression of functional genes which involved in soil microbial inorganic phosphate transportation ( phoR ), inorganic phosphate solubilization ( phoD , glpA , glpK , glpQ ), phosphate ester mineralization (gcd, ppk , ppx ), and phosphate ester mineralization ( pstABC , pit ) were also up-regulated in cotton-maize intercropping ( p < 0.05). Redundancy analysis showed that SOM, CaCl 2 -P and AP significantly correlated genes gcd, ppx , pstABC , pit , and phoD , suggesting that SOM, CaCl 2 -P and available P are important factors in influencing expression of these P-cycling functional genes. It is concluded that cotton-maize intercropping increased P bioavailability via changing rhizosphere soil microbial composition and functional genes.