Changes in pmoA Gene Containing Methanotrophic Population and Methane Oxidation Potential of Dry Deciduous Tropical Forest Soils

In natural ecosystems such as forests topographical gradients, species composition variability and seasonality, are the potential drivers of methane (CH₄) metabolism, and thus, of the population size and activities of methane oxidizing bacteria (MOB). To test the hypothesis that topography, tree species and seasonal variability influence MOB population and soil methane oxidation potential (MOP), we conducted two consecutive years of study selecting three sites in a dry deciduous tropical forest in Chandauli district of eastern Uttar Pradesh, India. The qPCR results showed a large variation in MOB population size (copies g⁻¹ dws), ranging from 1.0 × 10⁶ to 2.1 × 10⁷ and 9.0 × 10⁵ to 2.2 × 10⁷ during 2016 and 2017 respectively. The distribution of MOB population revealed the trend: hilltop > middle > hillbase with its maxima in the winter and minima in the rainy season. Laboratory incubation study revealed a similar trend in soil MOP (ng CH₄ g⁻¹ h⁻¹ dws), it varied from 10.6 to 20.6 and 10.5 to 20.7 during 2016 and 2017 respectively. The outer canopy soils showed lower MOB population and MOP compared to under canopy soils of tree species Butea monosperma, Madhuca indica and Tectona grandis during both years of study. The topography, season and tree species significantly influenced the MOB population size and MOP. Soil MOP showed a highly significant correlation (r = 0.89; p < 0.01) with MOB population, and a negative correlation was found with soil moisture (r = 0.76; p < 0.01). The results indicate that the dry deciduous tropical forest soils are potential sinks of atmospheric CH₄ wherein, the MOB population characteristically responds to topographical changes, tree species and seasonal shifts driving collectively the overall MOP of forest soils.