Effect of aquatic weeds on methane emission from submerged paddy soil.

Paddy fields are one of the dominant anthropogenic sources of methane emission to the atmosphere, and the main passageway of methane from paddy soil is through the rice plant. However, the effect of aquatic weeds on methane emission from rice paddies has not been properly evaluated yet. Methane emission from weeded pots and unweeded ones with anaerobic paddy soil was measured throughout the period of rice growth. More than double the amount of methane was emitted from weeded pots compared with unweeded ones. Peroxidase activity of rice root was not different between weeded and unweeded pots. However, methanogenic bacteria populations were higher in weeded pots than in unweeded ones, while methane oxidation activity, measured by the propylene oxidation technique, was higher in unweeded pots than in weeded ones. Methane oxidation activity of roots from three typical aquatic weeds in paddy fields, Lipocarpha sp., Rotala indica, and Ludwigia epilobioides, was higher than that of rice plants, while lower stems of these aquatic plants showed similar or lower activity compared with the same areas of rice plants. These results indicate that the role of aquatic weeds in paddy soil in methane emission should not be overlooked in evaluating mitigation options for reducing methane emission from paddy fields.