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

Abstract

The bacterial numbers and the composition of phospholipid fatty acids (PLF As) in the floodwater and the plow layer soil in a Japanese paddy field were compared during the rice cultivation period. The numbers of total and culturable bacteria ranged from 8.41×10⁵ to 1.72×10⁶ cells mL⁻¹ and 1.47×10⁴ to 8.49 × 10⁴ CFU mL⁻¹ in the floodwater, and 1.49×10⁹ to 4.31×10⁹ cells g^y−1 and 1.26 × 10⁷ to 3.89 × 10⁷ CFU g⁻¹ in the plow layer soil, 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 PLF As in the plow layer soil ranged from 25.8 to 55.5 μg g⁻¹ soil. The amount of PLFAs in the plow layer soil tended to increase just after midseason drainage. Dominant PLF As in the floodwater were 16 : 1ω7c, 16 : 0, and 18 : 1ω7, and those in the plow layer soil were 16 : 0,16 : 1ω7c, 18 : 1ω7,18 : 1ω9, il5 : 0, ail5 : 0, and 10Me17 : 0, respectively. The proportion of straight, mono-unsaturated PLFAs and branched PLFAs ranged from 33 to 48% and from 9 to 21% in the floodwater and from 28 to 33% and from 30 to 44% in the plow layer soil, respectively, suggesting the predominance of Gram-negative bacteria in the floodwater and Gram-positive bacteria in the plow layer soil. Principal component analysis of PLFA composition clearly revealed the difference in microbiota between the floodwater and plow layer soil. An indicator of the environmental stress imposed upon microbiota expressed by the trans vs. cis ratio of 16 : 1ω7 was consistently lower in the floodwater than in the plow layer soil.

Key Words:

• floodwater
• microbiota
• phospholipid fatty acids
• rice field
• stress factor