Impact of ryegrass cover crop inclusion on soil phosphorus and pqqC- and phoD-harboring bacterial communities

Italian ryegrass (Lolium multiflorum L.) is widely used as a cover crop with rice to promote soil fertility and reduce nutrient loss, although the specific impacts on phosphorus (P) dynamics and bioavailability are not clear. Soil samples were taken from a 4-year field experiment that included fertilized fallow-rice and ryegrass cover crop-rice rotations, together with an unfertilized fallow-rice control. Soil analyses included pH, total carbon (C) and nitrogen (N), together with soil P fractionations, acid and alkaline phosphatase enzyme activities, and assessment of the diversity and community of bacterial genes associated with inorganic P solubilization (pqqC) and organic P mineralization (phoD). Results showed that inclusion of the ryegrass cover crop enhanced biological P cycling in soil by significant increases in soil organic P and phosphatase enzyme activities compared with the fertilized fallow. The ryegrass cover crop was shown to reinforce the connection between soil P fractions and pqqC- and phoD-harboring bacterial communities, especially for the genus Rubrobacter. Cover crop inclusion also affected pqqC-harboring bacterial community composition by increasing the relative abundance of Actinobacteria, which reflected changes in the ratios of total P to total carbon and nitrogen in soil. In addition, the pqqC-harboring bacterial community was more affected by the ryegrass cover crop than the corresponding phoD-harboring community. The findings of this study demonstrated that the inclusion of ryegrass as a cover crop with rice significantly impacted biological P cycling in soil which may contribute to improved long-term P use efficiency.