Abstract: 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 (KPR₅₀) and 250 mg P/kg (KPR₂₅₀), mono-calcium phosphate (MCP) application at 50 mg P/kg (MCP₅₀), and the control without P application. The results showed that KPR₅₀, KPR₂₅₀, and MCP₅₀ 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 MCP₅₀, the relative effectiveness of KPR₅₀ and KPR₂₅₀ treatments in ryegrass production was about 23% and 68%, respectively. After one season of ryegrass growth, the KPR₅₀, KPR₂₅₀, and MCP₅₀ 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 KPR₂₅₀ and MCP₅₀ treatments compared with KPR₅₀ and control. The latter had no significant difference in the total or bacterial PLFAs. The KPR₅₀, KPR₂₅₀, and MCP₅₀ 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.

Key words: Phosphorus fractionation, Phospholipid fatty acid (PLFA), Ryegrass, Phosphate rock

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