Comparison of phospholipid fatty acid composition in floodwater and plow layer soil during the rice cultivation period in a Japanese paddy field

The bacterial numbers and the composition of phospholipid fatty acids (PLFA s) in the floodwater and the plow layer soil in a Japanese paddy held were compared during the rice cultivation period. The numbers of total and cultu rable bacteria ranged from 8.41x10(5) to 1.72x10(6) cells mL(-1) and 1.47x1 0(4) to 8.49x10(4) CFU mL(-1) in the floodwater, and 1.49x10(9) to 4.31x10( 9) cells g(-1) and 1.26x10(7) to 3.89x10(7) CFU g(-1) in the plow layer soi l, respectively. There was no appreciable seasonal variation in the number of bacteria either in the floodwater or in the plow layer soil. The amount of PLFAs in the plow layer soil ranged from 25.8 to 55.5 mug g(-1) soil. Th e amount of PLFAs in the plow layer soil tended to increase just after mids eason drainage. Dominant PLFAs in the floodwater were 16 : 1 omega 7c, 16 : 0, and 18 : 1 omega7, and those in the plow layer soil were 16 : 0, 16 : 1 omega 7c, 18 :1 omega7, 18 : 1 omega9, i15 : 0; ai15 : 0, and 10 Me17 : 0, respectively. The proportion of straight, mono-unsaturated PLFAs and branc hed PLFAs ranged from 33 to 48% and from 9 to 21% in the floodwater and fro m 28 to 33% and from 30 to 44% in the plow layer soil, respectively, sugges ting the predominance of Gram-negative bacteria in the floodwater and Gram- positive bacteria in the plow layer soil. Principal component analysis of P LFA composition clearly revealed the difference in microbiota between the f loodwater and plow layer soil. An indicator of the environmental stress imp osed upon microbiota expressed by the trans vs, cis ratio of 16 : 1 omega7 was consistently lower in the floodwater than in the plow layer soil.