Effects Of Different Rising Levels Of CO₂ Concentration On Respiration Rate And N₂O Flux In Rice And Wheat Fields

A series of ecological and environmental problems caused by the increasing concentration of atmospheric carbon dioxide?CO₂?have attracted extensive attention of many researchers.Farmland is an important part of the terrestrial ecosystem,and the concentration of atmospheric CO₂ continues to increase,which has a significant impact on the material circulation and energy flow of crops.As an important source and sink of CO₂and nitrous oxide?N₂O?in terrestrial ecosystem,rice and wheat rotation area is an important field of biogeochemical cycle research.In order to study the effect of rising atmospheric CO₂concentration on soil carbon and nitrogen cycling in farmland ecosystem in rice-wheat rotation region,field control experiments were carried out for five years.Three treatments were set in the experiment:CK,incremental?T₁?and sudden?T₂?.The test data in this paper were the data of rice and wheat rotation area test in 2018 and 2019.Among them,the concentration level of CO₂ treated by T₁ in winter wheat season and rice season was+80 ppm?CK+80,which was 80 ppm higher than that in the control group?and CK+120 ppm in the wheat season.Rice season CK+120 ppm,CK+160 ppm.The T₂treatment was 200 ppm higher each year than the control group,and 4 replicates were set for each treatment.The respiration rate and N₂O emission flux were calculated by static darkbox-gas box chromatography.The test results showed that:?1?Different CO₂ concentrations did not significantly change the seasonal variation patterns of respiration rate and N₂O emission in the growing season of winter wheat and rice.?2?In the growing season of winter wheat and rice,the positive correlation between respiration and soil temperature was observed.The relationship between N₂O flux and soil temperature was not obvious,and there was a temperature transition point of 18?in the wheat season.In the growing season of winter wheat,N₂O flux was positively correlated with soil moisture content,and the conversion point of soil moisture content was 0.25.?3?In the growing season of winter wheat,T₂ treatment increased the average respiration rate of soil at the green and jointing stages of wheat,and T₁ treatment significantly increased the average respiration rate of soil at the flowering and heading stages of wheat.In the rice season,T₂ treatment increased the average respiration rate of rice at the filling stage and the maturation stage,and T₁ treatment increased the average respiration rate of rice at the flowering stage and the maturation stage.T₁ and T₂ treatments did not significantly increase respiration accumulation in winter wheat and rice growing seasons.?4?In the winter wheat-rice growing season,T₁?CK+160 ppm?and T₂ treatment increased the average N₂O emission flux at the jointing stage of crops.The effects of T₁ and T₂ treatments on soil N₂O fluxes were different at different growth stages of wheat.The total effect of treatment at T₂?CK+160 ppm,CK+120 ppm?in the rice season was to promote the average N₂O flux of the system or reduce the absorption of N₂O in the atmosphere in the rice field.The cumulative N₂O emissions of winter wheat and rice were not significantly affected by different CO₂ treatments.?5?During the winter wheating-rice growing season,T₁ and T₂ treatments reduced plant height,stem sheath dry weight,leaf dry weight and root dry weight at the maturity stage.However,in other growth periods of rice and wheat,the results of different CO₂concentrations were different.?6?During the winter wheat-rice growing season,the content of ammonium nitrogen and nitrate nitrogen in the soil treated with T₁ and T₂ was higher than that of the control group but did not reach a significant level.Treatment with T₁and T₂ did not have significant effect on soil pH.