Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/1999
Publication Date: N/A
Citation: Interpretive Summary: Cultivation of rice under flooded soil conditions usually results in the emission of methane to the atmosphere. Methane is a greenhouse-effect gas that has a greater greenhouse warming potential than carbon dioxide. ARS-USDA scientists at Gainesville, FL in cooperation with scientists at Florida State University grew rice under elevated carbon dioxide expecting to find greater methane emissions, but instead we found less emissions. The only plausible way that this could happen is that the greater rooting density produced under elevated carbon dioxide led to greater oxygen diffusion from the atmosphere to the soil via air channels in the roots. Furthermore, this study may be unique because the low organic matter (less than 1 percent) of our soil would have caused very little demand for oxygen so that bacteria that feed on methane could have used almost all of it that was generated in the flooded soil.
Technical Abstract: Methane emissions from rice (Oryza sativa L., cvs. Lemont and IR-72) grown within Temperature Gradient Greenhouse Tunnels under doubled carbon dioxide (CO2) were only 2 to 10 percent of emissions from plants grown under ambient CO2. Methane emissions increased with a temperature increase of 2 degrees Celsius, from outdoors to the first cell of the ambient CO2 tunnel (ambient temperature plus 2 degrees Celsius). Within both tunnels and for both cultivars methane emissions decreased with further temperature increases (from 2 to 5 degrees Celsius above ambient). Carbon dioxide enrichment stimulated shoot and root production. Our original hypothesis was that increased CO2 would stimulate plant productivity and therefore stimulate methane emission, since direct linkages between these parameters have been observed. We concluded that CO2 enrichment decreased methane production due to increased delivery of oxygen to the rhizosphere because of increased root biomass and porosity. However, this study may be unique because the low organic content (less than 1 percent) of the sandy soil in which the rice was grown created very little oxygen demand.