Submitted to: Journal of Environmental Quality
Publication Type: Popular publication
Publication Acceptance Date: 12/28/2002
Publication Date: 3/28/2003
Citation: ALLEN JR, L.H., ALBRECHT, S.L., COLON, W., COVELL, S.A., BAKER, J.T., PAN, D., BOOTE, K.J. METHANE EMISSIONS OF RICE INCREASED BY ELEVATED CARBON DIOXIDE AND TEMPERATURE. JOURNAL OF ENVIRONMENTAL QUALITY. 2003. Interpretive Summary: Problem. Cultivation of paddy rice in water-saturated soil contributes large amounts of methane, a greenhouse gas, to the atmosphere. The capability of added methane to increase global warming is 21 times that of the same weight of carbon dioxide. Little is known about the direct effects of carbon dioxide and temperature on methane emissions of rice or other wetland plants. Accomplishment. ARS Scientists at Gainesville, Florida grew rice in flooded soil in carbon dioxide of either 330 or 660 PPM, and normal, +3 deg. C, and +6 deg. C warmer temperatures. The total methane emissions at 660 PPM were 3.8, 6.5, and 10.1 grams per square meter for normal +3 deg. C, and +6 deg. C, respectively, whereas the emissions at 330 PPM were 2.6, 3.0, and 5.4 grams per square meter for the same temperatures. Thus, methane emissions in 660 PPM and +6 deg. C were 4 times that in normal conditions. Usefulness. This study shows that both rising carbon dioxide and the anticipated global warming could cause an increase of methane emissions from rice and thus increase the warming by greenhouse gases even more. With this forewarning, scientists can develop methods to decrease methane emissions by paddy rice.
Technical Abstract: Cultivation of rice (Oryza sativa L.) Contributes large methane emissions (about 60 Tg/yr) to the atmosphere. We hypothesized that elevated carbon dioxide and temperature would increase emissions from paddy-culture rice; therefore, we grew tropical lowland rice (cv. IR72) in flooded soil with carbon dioxide atmospheres of either 33 or 66 Pa and temperatures that were normal, or +3 and +6 deg. Celsius warmer. Methane emissions were small up to 40 days after planting and increased afterward with highest emissions from the high carbon dioxide-high temperature treatment. Cumulative emissions by rice were 10.06, 6.46, and 3.83 g/m**2 for 38/29, 35/26, and 32/23 deg. Celsius, respectively, at 66 Pa, and 5.44, 2.97, and 2.58 g/m**2 for the same temperatures at 33 Pa. Methane emissions in doubled carbon dioxide at the highest temperature were 4 times that in ambient carbon dioxide at the lowest temperature. If natural wetlands, with emissions of about 115 Tg/yr, behave like rice, then we might expect even greater emissions of this greenhouse gas in the future. Since the greenhouse warming potential of added methane is currently 21 times that of added carbon dioxide on a mass basis, the implications for enhanced global warming are clear.