Effects of short-term conservation management practices on soil organic carbon fractions and microbial community composition under a rice-wheat rotation system

摘要

The objective of this study was to investigate the effects of short-term (less than 2 years) conservation managements no-tillage (NT) and crop residue returning on top soil (0-5 cm) microbial community composition and soil organic C (SOC) fractions under a rice-wheat rotation at Junchuan town of Hubei Province, China. Treatments were established following a split-plot design of a randomized complete block with tillage practices conventional tillage (CT) and NT as the main plot and residue returning level no residue returning (0) and all residues returned to fields from the preceding crop (S, 2,146 kg C ha(-1)) as the subplots. The four treatments were CT with or without residue returning (CT0 and CTS) and NT with or without residue returning (NT0 and NTS). The abundances of microbial groups total FLFAs, fungal biomass, bacterial biomass, fungal biomass/bacterial biomass (F/B), monounsaturated fatty acids/saturated fatty acids (MUFA/STFA), and microbial stress were determined by phospholipid fatty acid (PLFA) analysis of soil. The ratio of MUFA/STFA reflects aeration of soil and greater MUFA/STFA means better aeration condition of soil. Moreover, the microbial stress, the ratio of cy19:0 to 18:1 omega 7, was regarded as an indicator of physiological or nutritional stress of microbial community. PLFA profiles were dominated by the fatty acids iC15:0 (9.8 ), C16:0 (16.5 ), 10Me17:0 (9.9 ), and Cyc19:0 (8.3 ), together accounting for 44.6 of the total PLFAs. Compared with CT, NT significantly increased microbial biomass C (MBC) by 20.0 but did not affect concentrations of total organic C (TOC), dissolved organic C (DOC), easily oxidizable C (EOC), and SOC of aggregates. Residue returning significantly increased MBC by 18.3 and SOC content of 2-1-mm aggregate by 9.4 . NT significantly increased total PLFAs by 9.8 and fungal biomass by 40.8 but decreased MUFA/STFA by 15.5 . Residue returning significantly enhanced total PLFAs, bacterial biomass, fungal biomass, F/B, and MUFA/STFA by 31.1, 36.0, 95.9, 42.5, and 58.8 , respectively, but decreased microbial stress by 45.9 . Multivariate analysis (redundancy analysis and partial correlation analysis) indicated that SOC of 2-1-mm aggregate was related to changes in the composition of soil microbial groups, suggesting that SOC of 2-1-mm aggregate was sensitive to changes in soil microbial community composition affected by short-term conservation management practices in our study.