Effect Of Elevated Temperature And CO₂ Concentration,Nitrogen Application Rate On Greenhouse Gas Emissions In A Double Rice Cropping System

Increasing atmospheric carbon dioxide?CO₂?concentration and temperature,as main climatic factors,play an important role in driving methane?CH₄?and nitrous oxide?N₂O?emissions in rice field ecosystems.The application of nitrogen fertilizer is an important management practice to affect CH₄and N₂O emissions.In this study,we explored the characteristics of CH₄ and N₂O emissions in rice field ecosystems by simulating atmospheric CO₂ concentration and temperature of the Open top chamber?OTC?and setting different nitrogen fertilizer application gradient.Therefore,five treatments were selected:?1?UC:field environment;?2?CK?covering OTC?:consistent with the field CO₂ concentration and temperature;?3?ET?covering OTC?:temperature increase by 1.5?;?4?EC ?covering OTC?:CO₂ concentration increase by 100 ppm;?5?ETEC?covering OTC?:temperature and CO₂ concentration increase by 1.5?and 100 ppm,respectively.The experiment began in 2018 and each treatment was repeated 3 times.In 2009,conventional nitrogen fertilizer treatment(CN:180kg·N·hm^-2)and high nitrogen fertilizer treatment(HN:280 kg·N·hm^-2)was set up under each treatment.The emission rates of CH₄ and N₂O for early and late rice-growing season were observed by static box-gas chromatography in 2018 and 2019.The major findings obtained were as follows:?1?For CN treatment,the seasonal characteristics of CH₄ emission under ET,EC,and ETEC treatment were no different between 2018 and 2019.The CH₄ emissions were most emitted during the transplant-booting stage,with 87.8%-99.0%and 91.5%-97.4%of total emissions in early rice and late rice,respectively.The total emission of CH₄ in early rice of 2018 was higher than that of 2019 due to the temperature annual difference during the transplant-jointing period.The CH₄ emission under ET was not significantly changed compared with CK.EC and ETEC increased the total CH₄ emission during early rice?28.2%and 16.9%?and late rice?43.3%and 39.8%?.Compared with CN,HN did not change the emission characteristics of CH₄ between early rice and late rice.There was a significant difference for total CH₄ emissions under HN between early and late rice seasons.For early rice season,HN increased the total CH₄ emission by 2.6%,3.5%,12.5%,and 3.7%for CK,ET,EC,and ETEC,respectively,compared with CN.For late rice season,HN reduced total CH₄ emissions by 25.5%,14.0%,36.3%,and 32.2%for CK,ET,EC,and ETEC,respectively,compared with CN.?2?For CN,there were different characteristics of the N₂O emission between early and late rice.The N₂O emission of late rice was more concentrated than that of early rice.Compared with CK,the total emission of early rice and late rice under EC was increased by 36.5%and 57.6%,respectively.ET promoted the total N₂O emissions in early and late rice seasons.ETEC could increase the N₂O emission but did not significantly increase the N₂O emission compared with EC.Compared with CN,HN did not change the pattern of N₂O seasonal emission between early and late rice under CK,ET,EC,and ETEC.For early rice,the peak of N₂O emission under HN and CN appeared between the end of the tillering stage and 1 d after panicle fertilizer application?about 29-43 d after transplanting?.For late rice,the peak of N₂O emission under HN and CN was observed between drying stage?23-32 d after the transplanting?and 3d after panicle fertilization.The increase of nitrogen application in panicle stage promoted the N₂O emission of early and late rice.Compared with CN,HN increased the total emission of N₂O by 16.6%-57.8%and 85.6%-117.1%in early rice and late rice,respectively.The increase of late rice?85.6%-117.1%?was larger than that of early rice?16.6%-57.8%?.?3?For CN,the total greenhouse gas emissions?CO₂eq over a 100-year period?of early rice and late rice under EC was increased by 30.0%and 45.2%compared with CK,respectively.ET did not significantly change the total greenhouse gas emissions.ETEC increased the total greenhouse gas emissions of early rice?19.3%?and late rice?40.6%?.The total CO₂eq of greenhouse gas emissions may increase with the rise of atmospheric CO₂ concentration and temperature in the future.There are inter-annual differences between 2018 and 2019.Compared with CN,the total greenhouse gas emissions in early and late rice seasons under HN were different,which depended on the CH₄ emission.HN increased the total greenhouse gas emissions under CK,ET,EC,and ETEC in early rice and significantly decreased the total greenhouse gas emissions under EC in late rice.In summary,these findings proved the effects of increasing temperature,CO₂ concentration and nitrogen fertilizer application on CH₄ and N₂O emissions in double cropping ecosystem,providing initial data for the formulation of rational nitrogen application and greenhouse gas emission reduction strategies under future climate change.