Spatio-temporal variation and effect of urea fertilization on methanotrophs in a tropical dryland rice field

Population size of methanotrophs in a dryland field planted to Oryza sativa L. variety Narendra-118 was quantified over a period of 13 weeks. Methanot roph numbers were higher in control plots (52.9-736.6 x 10(5) cells g(-1) d ry soil) than in plots treated with urea (43.8-676.0 x 10(5) cells g(-1) dr y soil), and were highest in the rhizosphere soil (499.8-736.6 x 10(5) cell s g(-1) dry soil) followed by bulk (451.4-684.1 x 10(5) cells g(-1) dry soi l) and bare (43.8-67.5 x 10(5) cells g(-1) dry soil) soil. The concentratio ns of NH4+-N were significantly (P < 0.001) lower in the rhizosphere (3.1-6 .4 mu g g(-1) soil) than in bulk (4.1-8.3 mu g g(-1) soil) and bare soils ( 5.1-10.7 mu g g(-1) soil). The study suggests that the development of the r ice rhizosphere brings about a spatial pattern in the distribution of metha notrophic bacteria which increases in size, over time, within the rhizosphe re and adjoining bulk soil, and that the rhizosphere is a potential microsi te of intense CH4 exidation activity. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.