Effects of vegetation on the emission of methane from submerged paddy soil

Abstract

Methane emission rates from rice-vegetated paddy fields followed a seasonal pattern different to that of weed-covered or unvegetated fields. Presence of rice plants stimulated the emission of CH4 both in the laboratory and in the field. In unvegetated paddy fields CH4 was emitted almost exclusively by ebullition. By contrast, in rice-vegetated fields more than 90% of the CH4 emission was due to plant-mediated transport. Rice plants stimulated methanogenesis in the submerged soil, but also enhanced the CH4 oxidation rates within the rhizosphere so that only 23% of the produced CH4 was emitted. Gas bubbles in vegetated paddy soils contained lower CH4 mixing ratios than in unvegetated fiels. Weed plants were also efficient in mediating gas exchnage between submerged soil and atmosphere, but did not stimulate methanogenesis. Weed plants caused a relatively high redox potential in the submerged soil so that 95% of the produced CH4 was oxidized and did not reach the atmosphere. The emission of CH4 was stimulated, however, when the cultures were incubated under gas atmospheres containing acetylene or consisting of O2-free nitrogen.