The lowland paddy weed Monochoria vaginalis emits N2O but not CH4

Monochoria vaginalis is one of the most common and troublesome annual broadleaved weeds in rice paddies in Asia. It competes with rice for N uptake. Recent studies suggest that some plants can produce CH4 under aerobic conditions and some can produce N2O during nitrate assimilation. To test whether M. vaginalis emits either gas and hence is a significant contributor to greenhouse gas emissions, we grew plants in pots filled with paddy soil. CH4 and N2O emissions were not detected both from the M. vaginalis–soil system and from the aboveground plant tissues during 30- and 60-min sampling. In a 1-day incubation experiment in bottles, leaves, stems, and roots of M. vaginalis obviously emitted N2O but not CH4. Roots produced more N2O than leaves and stems, possibly owing to associated nitrifying or denitrifying bacteria. Therefore, we found no evidence of CH4 production, and possible evidence of slight N2O production in the tissues of M. vaginalis.