Effects of Gradually and Abruptly Elevated CO2 Concentration and Different Nitrogen Fertilizer Levels on CH4 Emission in Paddy Field
To explore the effects of gradually and abruptly elevated CO2 concentration and different nitrogen application levels on CH4 emissions in paddy field,a field rice(cv.Nanjing 9108)experiment was conducted based on the automatic CO2 concentration control platform,and CH4 flux was measured by static chamber-gas chromatography method.The experi-ment was designed as:the control(CK,ambient atmospheric CO2 concentration),a gradually elevated atmospheric CO2(C1,an increase of 40 μmol·mol-1 per year within 2016-2018),and an abruptly elevated atmospheric CO2(C2,an in-crease of 200 μmol·mol-1 directly).Meanwhile,a nitrogen fertilizer reduction treatment(N2,15 g·m-2)was set up in addition to the conventional nitrogen application amount(N1,25 g·m-2).The results show that the seasonal variation of CH4 fluxes was not significantly changed under different CO2 concentrations and nitrogen treatments,and CH4 fluxes showed a trend of increasing first and then decreasing.During the whole growth period of rice,C1 and C2 treatments had no significant effects on CH4 emission per unit yield.Under C2 condition,compared with N1 treatment,N2 treatment signifi-cantly reduced rice yield by 45.2%(P=0.037),and significantly increased CH4 emission per unit yield by 63.3%(P= 0.008).Overall,under the elevated CO2 concentration,nitrogen fertilizer reduction treatment(15 g·m-2)reduced rice yield and simultaneously increased CH4 emission per unit yield.
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