Seasonal variations of phospholipid fatty acid composition in the floodwater of a Japanese paddy field under a long-term fertilizer trial

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Abstract
The concentration and composition of phospholipid fatty acids (PLFAs) in the floodwater of a Japanese paddy field under a long-term fertilizer trial for more than 70 y [no fertilizers (NoF) plot, chemical fertilizers (CF) plot, chemical fertilizers and composts (CM) plot] were determined. The amount of PLFAs ranged from 2.8 to 14.1 μg L-1 for the NoF plot, from 3.2 to 8.6 μg L-1 for the CF plot, from 4.4 to 13.0 μg L-1 for the CM plot, respectively. Dominant PLFAs in the floodwater were 16: lω7, 16: 0, 18: 1ω7 in all the plots. Straight, mono-unsaturated PLFAs accounted for about 40% of the total, suggesting the predominance of Gram-negative bacteria in the floodwater. Principal component analysis and cluster analysis of PLFA composition clearly revealed the variations of microbiota in the floodwater with the kinds of fertilizer and the growth stages of rice plants. An indicator of the environmental stress imposed upon microbiota expressed by the trans vs. cis ratio of 16: 1ω7 was consistently low, indicating that the floodwater environment was a low-stress environment upon the microbiota.