Microbiota responsible for the decomposition of rice straw in a submerged paddy soil estimated from phospholipid fatty acid composition

To identify the microbiota responsible for rice straw decomposition in submerged paddy soils, phospholipid fatty acids (PLFAs) in decomposing rice straw (RS) under submerged incubation conditions with changes in the incubation temperature (22 and 30 degreesC) and nitrogen status (without N amendment, and with ammonium sulfate or urea amendment) were determined. Straight, saturated PLFAs, especially 16: 0 PLFA, predominated in the RS before decomposition in soil, and they accounted for 65% of the total PLFAs in RS, followed by straight, mono-unsaturated PLFAs (27%). The percentages of straight, saturated PLFAs and straight, mono-unsaturated PLFAs in RS decreased with the decomposition to the levels of 36 to 44% for the straight, saturated PLFAs and of 12 to 16% for the straight, mono-unsaturated PLFAs, while the percentages of branched-chain PLFAs increased markedly from 2% to the level of 40 to 46%, irrespective of the incubation temperature and nitrogen status, which indicated that Gram-positive bacteria were mainly responsible for the RS decomposition in the submerged paddy soil. Microbial succession in the decomposition process of RS was inferred based on cluster analysis and principal component analysis. The stress factor estimated from the trans/cis ratio of 16: 1 omega7 PLFA in the RS undergoing decomposition ranged from 0.21 to 0.40 at 22 degreesC, and from 0.27 to 0.58 at 30 degreesC irrespective of the nitrogen status, indicating that decomposing RS was a highly stressed environment for the microorganisms inhabiting within RS.