| Much attention has been paid to the atmospheric greenhouse gases(GHGs), such as CO2, CH4and N2O, which contributed to global warming and ozone depletion. Agroecosystems are main souces of GHGs emissions. Effects of elevated atmospheric CO2and temperature on CH4and N2O emissions from rice rice-wheat rotations in Tai lake region were examined under a T-FACE(distinguished by elevated CO2concentration and increased temperature) experimental station. The fluxes of CH4and N2O emission from rice-wheat rotations were measured using static opaque chamber-gas chromatograph techniques.In this study, field experiments were accomplished over one rice-wheat rotation cycles. In2011, we measured CH4and N2O fluxes under a T-FACE(elevated CO2concentration, C; increased temperature, T; elevated CO2concentration and increased temperature, CT) experimental station.The results of this study are displayed as follows:1. The cumulative CH4emissions were increased under the conditions of high CO2concentrations and increased temperature, and the stimulating effects on CH4fluxes were followed as the order of C(elevated CO2concentration)>CT(elevated CO2concentration and increased temperature)>T(increased temperature). As compared to the plots without rice plantation, CH4emissions were enhanced under the plots with rice plantation. Seasonal fluxes of CH4from the plots with or without rice plantation averaged1.88and1.08mg·m-2·h-1, respectively. C, CT and T treatment of CH4seasonal fluxes from the rice-involved plots averaged6.99mg·m-2·h-1,3.87mg·m-2·h-1and2.99mg·m-2·h-1, while the rice-uninvolved plots averaged4.50mg-m-2-h-1,2.61mg-m-2·h-1and1.94mg·m-2·h-1respectively. In contrast with the control, CH4emissions from the C, CT and T treatments were increased by273%,106%and59%for the rice-planted plots, while they were increased by317%,142%and79%for the plots without rice plantation, respectively(P<0.05).2. As compared to the plots without rice plantation, N2O emissions were increased by53%under the plots with rice plantation. Seasonal fluxes of N2O from the plots with or without rice plantation averaged207.21μg·m-2·h"1and135.51μg·m-2·h-1, respectively. C, CT and T treatment of N2O seasonal fluxes from the rice-involved plots averaged331.10μg·m-2·h-1,266.06μg·m-2·h-1and193.87μg·m-2·h-1, while the rice-uninvolved plots averaged236.11μg·m-2·h-1,199.4μg·m-2·h-1and151.78μg·m-2·h-1, respectively. In contrast with the control, N2O emissions from the C and CT treatments were increased by62%and29%for the rice-planted plots, while they were increased by74%and45%for the plots without rice plantation, respectively(P<0.05). T treatments were decreased by7%for the rice-planted plots, while they were increased by11%for the plots without rice plantation, respectively. Total N2O emissions for the plots without rice plantation were significantly affected by T treatments, but the effects of T treatments and CK treatments were not significant for the plots with rice plantation.3. The cumulative N2O emissions were increased under the conditions of high CO2concentrations and increased temperature, especially for C treatment. In contrast with the control, N2O emissions from the C, CT and T treatments were increased by26%,5%and1%for the wheat-planted plots, while they were increased by24%,11%and6%for the plots without wheat plantation, respectively(P<0.05). As compared to the plots without wheat plantation, N2O emissions were enhanced under the plots with rice plantation. C, CT and T treatment of N2O seasonal fluxes from the rice-involved plots averaged406.12μg·m-·h-1,337.94μg·m-2·h-1and325.66μg·m-2·h-1, while the rice-uninvolved plots averaged376.20μg·m-2·h-1,335.89μg·m-2·h-1and332.33μg·m-2·h-1respectively. As compared to the plots without wheat plantation, N2O emissions were increased from10.08kg ha-1to10.71kg ha-1under the plots with rice plantation.4. The CH4and N2O emissions across the annual rice-wheat cropping rotation were significantly correlated to crop. Compared with the control, elevated atmospheric CO2and increased temperature increased rice biomass by24%,7%and16%for the C, CT and T treatments, respectively. Significant linear relationships were found between seasonal CH4emission and rice biomass. There were also significant linear relationships between seasonal N2O emission and rice biomass. There were almost having no CH4emissions in wheat growing season, and growing wheat increased N2O emission. Growing rice increased N2O emission by53%, while growing wheat increased N2O emission by6%. Relative to the plots without crop plantation, the plots with crop plantation increased the GWPs by62%(P<0.05) and6%(P=0.07) over the100-year horizon for rice and wheat season. For the rice-wheat cropping rotation, the plots with crop plantation increased the GWPs by28%. In conclusion:First, the cumulative CH4emissions were increased under the conditions of high CO2concentrations and increased temperature, especially for C treatment. There was almost having no CH4emissions in wheat growing season. Second, all treatment could increase N2O emissions, except for T treatment under the plots with rice plantation. Finally, the CH4and N2O emissions across the annual rice-wheat cropping rotation were significantly correlated to crop. Significant linear relationships were found between seasonal CH4and N2O emission and rice biomass. Growing rice and wheat could increase N2O emission, while the increasing rates of growing rice was large than wheat. Relative to the plots without crop plantation, the plots with crop plantation increased the net GWPs for the rice-wheat cropping rotation. |
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