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TECHNICAL REPORTS

Atmospheric Pollutants and Trace Gases

Methane Emissions of Rice Increased by Elevated Carbon Dioxide and Temperature

^a USDA Agricultural Research Service and Agronomy Department, University of Florida, P.O. Box 110965, Gainesville, FL 32611-0965
^b USDA Agricultural Research Service, Columbia Plateau Conservation Research Center, P.O. Box 370, Pendleton, OR 97801
^c School of Science and Technology, Universidad del Este, P.O. Box 2010, Carolina, Puerto Rico 00984-2010
^d Environmental Planning Branch, Air National Guard Readiness Center, 3500 Fetchet Ave., Andrews Air Force Base, MD 20762
^e USDA Agricultural Research Service, Cropping Systems Research Laboratory, Big Spring, TX 79720
^f Agronomy Department, University of Florida, P.O. Box 110500, Gainesville, FL 32611-0500

^* Corresponding author (lhajr{at}mail.ifas.ufl.edu or lallen{at}gainesville.usda.ufl.edu).

Received for publication October 28, 2002. Methane (CH₄) effluxes by paddy-culture rice (Oryza sativa L.) contribute about 16% of the total anthropogenic emissions. Since radiative forcing of CH₄ at current atmospheric concentrations is 21 times greater on a per mole basis than that of carbon dioxide (CO₂), it is imperative that the impact of global change on rice CH₄ emissions be evaluated. Rice (cv. IR72) was planted in sunlit, closed-circulation, controlled-environment chambers in which CH₄ efflux densities were measured daily. The CO₂ concentration was maintained at either 330 or 660 µmol mol^-1. Air temperatures were controlled to daily maxima and minima of 32/23, 35/26, and 38/29°C at each CO₂ treatment. Emissions of CH₄ each day were determined during a 4-h period after venting and resealing the chambers at 0800 h. Diurnal CH₄ effluxes on 77, 98, and 119 d after planting (DAP) were obtained similarly at 4-h intervals. Emissions over four-plant hills and over flooded bare soil were measured at 53, 63, and 100 DAP. Emissions were negligible before 40 DAP. Thereafter, emissions were observed first in high-CO₂, high-temperature treatments and reached a sustained maximum efflux density of about 7 mg m^-2 h^-1 (0.17 g m^-2 d^-1) near the end of the growing season. Total seasonal CH₄ emission was fourfold greater for high-CO₂, high-temperature treatments than for the low-CO₂, low-temperature treatment, probably due to more root sloughing or exudates, since about sixfold more acetate was found in the soil at 71 DAP. Both rising CO₂ and increasing temperatures could lead to a positive feedback on global warming by increasing the emissions of CH₄ from rice.

Abbreviations: DAP, days after planting • SPAR, Soil–Plant–Atmosphere Research

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JEQ 2003 32: 1931-1938. [Full Text]