Rice fields are one of the major biogenic sources of atmospheric methane. Apart from this contribution to the greenhouse effect, rice paddy soil represents a suitable model system to study fundamental aspects of microbial ecology, such as diversity, structure and dynamics of microbial communities as well as structure function relationships between microbial groups. The present study was conducted in rainfed rice fields planted to rice (Oryza sativa) cultivar, NDR-97, to evaluate the variation of population of Methane Oxidizing Bacteria (MOB) in different soil type (Bare, Bulk and rhizosphere) over a period of 13 weeks. Urea was the only fertilizer applied, at a rate of 100 kg N ha-1 in three split doses. The experiment was laid out in a randomized complete block design with three replicate plots for treatments. The soil exhibited higher numbers of MOB in control plots of bulk and rhizospheric (37.4x106 and 58.87x106 cells g-1 dry soil) than in plots treated with urea (28.6x106 and 51.9x106 cells g-1 dry soil) at 80 Days after Sowing (DAS) and were highest in the rhizospheric soil (58.87x106 cells g-1 dry soil) followed by bulk (37.4x106 cells g-1 dry soil) and bare (2.2x106 cells g-1 dry soil) in unfertilized soil but bare (control) soil was attained highest MOB (2.7x106 cells g-1 dry soil) on 40 DAS and MOB significantly decreased in fertilized soil. The concentrations of NH4+-N were significantly (p<0.05) lower in the rhizosphere (1.3 μg g-1 soil) than in bulk (3.7 μg g-1 soil) and bare soils (4.1 μg g-1 soil) on 80 DAS in unfertilized plots. In fertilized soil NH4+-N concentration were increased due to lower number of population at different days intervals. 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 methanotrophic bacterial activity.
B. Singh, D. Katiyar, D.V. Singh, A.K. Kashyap and A.M. Lall, 2011. Impact of Urea on Spatio-temporal Distribution of Methanotrophic Bacteria in Rainfed Rice Agro Ecosystem. International Journal of Agricultural Research, 6: 699-706.