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

Summary 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.