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

Abstract

Population size of methanotrophs in a dryland field planted to Oryza sativa L. variety Narendra-118 was quantified over a period of 13 weeks. Methanotroph numbers were higher in control plots (52.9-736.6×10⁵ cells g⁻¹ dry soil) than in plots treated with urea (43.8-676.0×10⁵ cells g⁻¹ dry soil), and were highest in the rhizosphere soil 9499.8-736.6×105 cells g⁻¹ dry soil) followed by bulk (451.4-684.1×10⁵ cells g⁻¹ dry soil) and bare (43.8-67.5×10⁵ cells g⁻¹ dry soil) soil. The concentrations of NH₄⁺-N were significantly (P<0.001) lower in the rhizosphere (3.1-6.4 μg g⁻¹ soil) than in bulk (4.1-8.3 μg g⁻¹ soil) and bare soils (5.1-10.7 μg g⁻¹ soil). The study suggests that the development of the rice rhizosphere brings about a spatial pattern in the distribution of methanotrophic bacteria which increases in size, over time, within the rhizosphere and adjoining bulk soil, and that the rhizosphere is a potential microsite of intense CH₄ oxidation activity.