Effect of CO2 enrichment and elevated temperature on methane emissions from rice, Oryza sativa

Methane emissions from rice grown within Temperature Gradient Greenhouse Tunnels under doubled CO2 concentrations were 10-45 times less than emissions from control plants grown under ambient CO2. For two cultivars of rice (cvs. Lemont and IR-72), methane emissions increased with a temperature increase of 2 degrees, from outdoor ambient temperatures to the first cell of the ambient CO2 tunnel (ambient temperature + 2 degrees C). Within both tunnels and for both cultivars methane emissions decreased with further temperature increases (from 2 degrees to 5 degrees C above ambient). Carbon dioxide enrichment stimulated both above- and below-ground 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 hypothesize that CO2 enrichment led to the attenuation of methane production due to increased delivery of oxygen to the rhizosphere because of increased root biomass and porosity. The increased root biomass due to elevated CO2 may have more effectively aerated the soil, suppressing methane production. However, this study may be unique because the low organic content (<1%) of the sandy soils in which the rice was grown created very little oxygen demand.