The changes in soil microbial community are supposed to be one of key factors for peanut yield decline in long-term continuous monocropping systems. A series of peanut fields, where peanut were continuously monocropped for 3, 6, 10 and 15 years in subtropical China, were selected to investigate the effect of continuous monocropping on peanut yield, soil microbial community structure and enzyme activity. Peanut yield, urease and invertase activities decreased with time, but the activity of polyphenol oxidase decreased in the first several years and then increased. The results of both culture dependent methods and phospholipid fatty acids (PLFA) analysis showed that bacteria (Gram-positive and Gram-negative bacteria) and actinomycetes decreased, while fungal colony-forming units (CFUs) increased with time. Canonical Correspondence Analysis (CCA) showed that with increasing peanut monocropping years, soil microbial structure became more correlative with fungi compositions. The proportion of bacteria in total PLFA decreased from 67.4% to 53.0%, meanwhile the proportion of fungi was increased from 16.9% to 32.8%. Denaturing gradient gel electrophoresis (DGGE) analysis indicated that bacteria diversity decreased and fungi diversity increased with time, and changes in fungi diversity were much greater than those of bacteria.
Key words: DGGE, enzyme activities, monocropping, peanut, PLFA, red soil.
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