The effect of soil type and plant age on the population size of rhizospheric methanotrophs and their activities in tropical rice soils.

A laboratory incubation experiment was conducted in tropical rain-fed (red soil) and irrigated (black soil) rice agroecosystem during the crop growing season to determine the effect of the type of soil, cultivation practices and the age of plant on MOB (methane oxidizing bacteria) population size and their activities. The average value of MOB population size was 11.7 +/- 4.5 x 10(5) cells g(-1) soil, with a range of 3.1 +/- 0.4 to 21.2 +/- 1.0 x 10(5) cells g(-1) soil for red soil, which was lower in comparison to black soil where population size varied between 84.2 +/- 3.8 and 289.4 +/- 7.0 x 10(5) cells g(-1) soil with an average of 182.8 +/- 53.5 x 10(5) cells g(-1) soil. The highest population size was recorded during the grain maturation stage which gradually declined during the grain filling, flowering and tillering stages of the rice plants. The HSD test indicated a significant variation in the MOB population size with the varying ages of the plant. CH4 oxidizing capacity was higher in black soil as compared to red soil. The highest CH4 oxidizing capacity was found at the grain-filling stage in both the soil types. The differences in soil types and cultivation practices, pattern of variation in MOB population size and methane oxidation were found similar in both the sites under the influence of plant age, even though the detected values differed significantly.