Plant-induced spatial variations in the size of methanotrophic population in dryland and flooded rice agroecosystems

Population size of methanotrophs was enumerated for rhizospheric, bulk and bare soils of a dryland and a flooded rice agroecosystem of Gangetic Plains . Measurements were made for two consecutive years (1997 and 1998). The pop ulation size in flooded rice plots was smaller than in the dryland rice plo ts. In dryland and flooded rice plots during both the years, population siz e of methanotrophs followed the order rhizosphere > bulk > bare soil. Conce ntrations of available N (NH4+-N and mineral-N) followed a reverse trend (r hizosphere < bulk < bare soil). The methane oxidizing bacterial population size was inversely related to the NH4+-N content of the soil. The spatial p attern of the MOB population size was more or less similar in dryland and f looded rice soils and underlined the importance of rhizosphere conditions a nd plant development in both ecosystems.