Phosphorus status and microbial community of paddy soil with the growth of annual ryegrass (Lolium multiflorum Lam.) under different phosphorus fertilizer treatments.

Annual ryegrass (Lolium multiflorum Lam.) was grown in paddy soil in pots under different phosphorus (P) fertilizer treatments to investigate changes of P fractions and microbial community of the soil. The treatments included Kunyang phosphate rock (KPR) applications at 50 mg P/kg (KPR(50)) and 250 mg P/kg (KPR(250)), mono-calcium phosphate (MCP) application at 50 mg P/kg (MCP(50)), and the control without P application. The results showed that KPR(50), KPR(250), and MCP(50) applications significantly increased the dry weight of the ryegrass by 13%, 38%, and 55%, and increased P uptake by 19%, 135%, and 324%, respectively. Compared with MCP(50), the relative effectiveness of KPR(50) and KPR(250) treatments in ryegrass production was about 23% and 68%, respectively. After one season of ryegrass growth, the KPR(50), KPR(250), and MCP(50) applications increased soil-available P by 13.4%, 26.8%, and 55.2%, respectively. More than 80% of the applied KPR-P remained as HCl-P fraction in the soil. Phospholipid fatty acid (PLFA) analysis showed that the total and bacterial PLFAs were significantly higher in the soils with KPR(250) and MCP(50) treatments compared with KPR(50) and control. The latter had no significant difference in the total or bacterial PLFAs. The KPR(50), KPR(250), and MCP(50) treatments increased fungal PLFA by 69%, 103%, and 69%, respectively. Both the principal component analysis and the cluster analysis of the PLFA data suggest that P treatments altered the microbial community composition of the soils, and that P availability might be an important contributor to the changes in the microbial community structure during the ryegrass growth in the paddy soils.