Abstract: We investigated the influence of longterm fertilizations on microbial community structure and functional diversity after 20 years of inorganic and organic fertilizer applications to a red paddy soil converted from an infertile wasteland, based on examining the phospholipid fatty acid (PLFA) profiles and community level physiological profiles (BIOLOG) of microorganisms. The relationship between microbial indicators and soil nutrient contents was also analyzed. After 20 years of cultivation, P fertilizer application increased total rice yield, soil organic C, total N, available N, total P and available P by 196.6%, 11.4%, 19.4%, 14.0%, 100.6% and 300.1% on average compared with Pomitted treatments, while organic manure application increased those by 85.4%, 23.8%, 25.0%, 15.0%, 38.6% and 86.8% on average compared with organic manureomitted treatments. Total microbial PLFA was 13.6%-68.9% higher in P fertilizer and organic manure application treatments than in no fertilizer treatment. Phosphorus fertilizer and organic manure application also increased PLFA of all microbial taxonomic groups. Average well color development (AWCD) values, Shannon index, Simpson index and McIntosh index of microbial community under the different treatments was 0.17-0.30, 2.79-3.03, 0.93-0.94 and 1.46-2.27, respectively. The application of P fertilizer and organic manure increased AWCD values and all microbial indices of microbial community. Principal component analysis showed that PLFA profiles and C source utilization patterns in treatments with P fertilizer and organic manure were clearly different from that in no fertilizer treatment, N treatment and NK treatment. Stepwise regression analysis revealed that soil organic C, total P, total N and available P significantly affected PLFA profiles and microbial functional diversity. The application of P fertilizer and organic manure could help promote soil microbial activity and diversity, and increase soil biological function and productivity.

Key words: soil enzyme activity, cropping system, straw management, soil organic carbon, soil quality.