Microbial ecology of methane emission in rice agroecosystem: a review

TLDR: It has now become possible to isolate, detect and characterize the methanogens and methanotrophs by using molecular biological tools like PCR, FISH, etc.

Abstract: Methane has profound impact on the physico-chemical properties in atmosphere leading to global climate change. Out of the various sources of CH4, rice fields are the most significant contributors. The processes involved in the emission of CH4 from rice fields to the atmosphere include CH4 production (methanogenesis) in the soil by methanogens, methane oxidation (methanotrophy) by methanotrophs and vertical transfer of CH4 via plant transport and diffusion or ebullition. In the overall methane dynamics rice plants act as : a) source of methanogenic substrate, b) conduit for CH4 through well developed system of inter cellular air space (aerenchyma), and c) potential methane oxidizing micro-habitat in the rhizosphere by diffusing oxygen which favour the growth and multiplication of methanotrophs. Apart from mechanistic uncertainties, there are several other uncertainties in the estimation of CH4 flux. Methane dynamics in the paddy field is controlled by a complex set of parameters linking the biological and physical characteristics of soil environment like temperature, carbon source, Eh, pH, soil microbes and properties of rice plants, etc. It has now become possible to isolate, detect and characterize the methanogens and methanotrophs by using molecular biological tools like PCR, FISH, etc. techniques. The apparent half saturation constant (Km) and maximum oxidation rate (Vmax) are distinctive parameters which determine the ability of bacteria to survive on atmospheric methane. Keywords. methane; methanotrophs; methanotrophy; methanogens; molecular tools