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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

View larger version (25K): [in a new window]   Fig. 1. Redox potentials at a depth of 0.20 m in the soil of each of the lysimeters (relative to a saturated calomel reference electrode placed in the flood water).

View larger version (29K): [in a new window]   Fig. 2. Season-long CH4 emission from flooded-soil rice culture at 330 and 660 µmol mol-1 CO2 concentrations and 32/23, 35/26, and 38/29°C day–night maximum and minimum air temperatures. Data are daily emission rates averaged over weekly periods.

View larger version (35K): [in a new window]   Fig. 3. Diurnal CH4 emission at 78 and 99 d after planting (DAP) from flooded-soil rice culture at 330 and 660 µmol mol-1 CO2 concentrations and 38/29°C day–night maximum and minimum air temperatures (labeled 38°C). Data are shown from duplicate chambers.

View larger version (34K): [in a new window]   Fig. 4. Diurnal CH4 emission at 78 and 99 d after planting (DAP) from flooded-soil rice culture at 330 and 660 µmol mol-1 CO2 concentrations and 35/26 and 32/23°C day–night maximum and minimum air temperatures (labeled 35°C and 32°C, respectively).

View larger version (36K): [in a new window]   Fig. 5. Diurnal CH4 emission rates from an intact plant canopy at 121 d after planting (DAP) and from stubble after cutting at 139 DAP at 330 and 660 µmol mol-1 CO2 concentrations and 38/29°C day–night maximum and minimum air temperatures (labeled 38°C). Data are shown from duplicate chambers.

View larger version (35K): [in a new window]   Fig. 6. Diurnal CH4 emission rates from an intact plant canopy at 121 d after planting (DAP) and from cut stubble at 139 DAP at 330 and 660 µmol mol-1 CO2 concentrations and 35/26 and 32/23°C day–night maximum and minimum air temperatures (labeled 35°C and 32°C, respectively).

View larger version (29K): [in a new window]   Fig. 7. Rice root biomass (top panel) and root length density (bottom panel) at 5-cm depth increments sampled at 70 d after planting from a cluster of four plants growing in 20-cm-diameter cylindrical pots in the Soil–Plant–Atmosphere Research (SPAR) chambers at two CO2 concentrations and three temperature regimes. Values for 330 µmol mol-1 in solid bars are plotted over values for 660 µmol mol-1 in hatched bars. Across three samplings during the season, root length density (cm cm-3) at the 0- to 5-cm soil depth = 0.264 + 4.32 x root biomass (g); r2 = 0.99.

View larger version (23K): [in a new window]   Fig. 8. Total seasonal CH4 emissions versus total seasonal photosynthetic CO2 uptake of rice for two CO2 and three temperature treatments. Within each CO2 treatment, the data points increase in magnitude within increasing temperature treatments of 32/23, 35/26, and 38/29°C, respectively.