CH₄ Flux Characteristics And Simulation Study Of Rice-wheat Rotation Farmland Ecosystem In Huaihe River Basi

Methane（CH₄）is the second most important greenhouse gas in the world with its extremely high warming potential,and it is one of the main factors affecting global warming.Rice-wheat rotation farmlands are important sources of CH₄ emissions.As the main production area of rice and winter wheat in China,the Huai River Basin agroecosystems have an important impact on the CH₄ fluxes of China.It is of great significance for the sustainable development of Chinese agriculture to accurately evaluate the spatiotemporal characteristics of CH₄ fluxes,and to formulate scientific CH₄ reduction measures in the rice-wheat rotation farmlands in the basin.This paper takes the rice-wheat rotation farmlands in the Huai River Basin as the research object,and uses the CH₄ flux observation data from the Shouxian National Climatology Site（2019-2021）to analyze the characteristics and controlling factors of the CH₄ fluxes in the typical rice-wheat rotation farmland in the Huai River Basin.At the same time,based on the DNDC（De Nitrification-De Composition）model after parameter calibration,the CH₄ fluxes and their spatiotemporal characteristics of rice-wheat rotation farmlands in the Huai River Basin from 2000 to 2020 were estimated,the CH₄ fluxes and their spatiotemporal characteristics from 2021 to 2049 were also estimated under two future climate change scenarios（RCP4.5,RCP8.5）.The farmland CH₄ reduction capacity of various field management measures in the basin was evaluated under the future climate change scenarios.The main conclusions are as follows:（1）The CH₄ fluxes showed an obvious single-peak diurnal variation,and the peak value appeared in the afternoon.The CH₄ fluxes also showed significant seasonal variations.Compared with the rice growing season,the CH₄ fluxes in the wheat growing season was almost negligible.In the rice growing season,the CH₄ fluxes increased significantly with the increase of air temperature（T_a）,and decreased significantly with the increase of vapor pressure deficit（VPD）.（2）The average regional CH₄ flux in the Huai River Basin which performed as a CH₄source from 2000 to 2020 was 125.3 kg/ha,and this value showed a fluctuating upward trend.CH₄ flux showed higher values in the south and northwest regions,and lower values in the northeast and central-western regions.Compared with 2000s,the CH₄ fluxes in 2010s had a significant increase,with large changes around 34.5°N and 32.5°N.（3）Under the RCP4.5 and RCP8.5 scenarios,the CH₄ fluxes in the Huai River Basin would fluctuate and increase in 2021-2049.The average regional CH₄ flux is 140.5 kg/ha and 150.5 kg/ha respectively.Compared with 2010s,the average regional CH₄ flux increased by 12%and 20%respectively.Under these two scenarios,the impact of climate change on the central and southern regions was more significant than that on the northeast.（4）Under RCP4.5（RCP8.5）scenario,10%and 20%reduction of fertilizer application（S0F1,S0F2）can reduce CH₄ emissions by 3.6%（3.7%）and 7.9%（7.8%）,respectively.50%and 100%of residue rate（S1F0,S2F0）can increase CH₄ emissions by146.2%（146.6%）and 235.8%（238.2%）,respectively.The regional CH₄ fluxes under all measures were higher in the south and northwest,and lower in the northeast and central-western regions.In consideration of the carbon emission situation in the Huai River Basin,the best field management measure was none residue to the field+reducing fertilizer by 20%under the future climate change scenario.