Contrasting pattern of methanotrophs in dry tropical forest soils: effect of soil nitrogen, carbon and moisture.

Population dynamics of methane-oxidizing bacteria (MOB) was measured for 2 consecutive years for four forest and one savanna sites in seasonally dry tropical regions of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of soils. There were significant differences in MOB population size during the 2 years (mean 0.40 and 0.48 x 10(5) cells g(-1) dry soil), and at different sites (mean 0.38-0.59 x 10(5) cells g(-1) dry soil). The mean population size of MOB was higher (P<0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and MOB population size during summer (the driest period) and a negative relation during the rest of the year. The number of MOB was consistently higher for the Kotwa hill base site than rest of the sites having higher soil organic C and total N. The results suggested that in seasonally dry tropical forests the moisture, C and N status of the soil regulates the population size of MOB (methanotrophs) in the long term.