| CH4 has become the world's second largest greenhouse gas with its extremely high warming potential,and plays an important role in global climate change.Paddy fields are an important source of CH4 emissions.As the main production area for rice cultivation in China,the Taihu Lake Basin's contribution to CH4 emissions from rice fields in China cannot be underestimated.How to accurately assess and slow down CH4emissions from rice fields is of great significance for sustainable agricultural development.In view of this,this study selects the rice-wheat rotation farmland ecosystem in the Taihu Lake Basin,and conducts field observations of CH4 flux at a point scale,reveals the characteristics and influencing factors of CH4 emission.Based on this,the parameter calibration and accuracy verification of the DNDC ecosystem model were carried out,and then the CH4 emission from rice fields in the Taihu Lake Basin from 1985 to 2017 was simulated to clarify the temporal and spatial evolution pattern of CH4 emissions from rice fields in the Taihu Lake Basin.Immediately afterwards,different management models of fertilization and straw return were combined into 16 scenarios to simulate CH4 emissions from rice fields in the Taihu Lake Basin from 2018 to 2035,and to evaluate the comprehensive impact of different management models on CH4 emissions,with a view to the Taihu Lake Basin agricultural ecosystem CH4 emission assessment and emission reduction policy formulation provide theoretical basis,scientific methods and technical support.The main results are as follows:(1)The diurnal variation in CH4 emission during the rice season appears under two modes:irregular and unimodal.In the irregular mode,CH4 emission was unstable throughout the day,and in the unimodal mode,the emissions during the day were significantly higher than that at night.The emission of CH4 in the rice season is concentrated in the early and middle stages of rice growth,relatively weak in the later stage,relatively low in the green stage,strong in the tillering stage,and lowest in the maturity stage.(2)CH4 emission of the rice season in the typical rice-wheat rotation area of the Taihu Lake Basin has an exponential relationship with air temperature,soil temperature,soil moisture of 10 and 20 cm,a quadratic relationship with soil moisture of 40 cm,and a power relationship with soil electrical conductivi-ty.CH4 emission and friction wind speed are only significantly correlated on a half-hour scale.Semi-empirical multiplication model:FCH4=0.006·580.8Tsi·0.126Ui*·197.2VWCi·0.003ECisimulates CH4 emissions well.(3)In terms of time change,the total CH4 emission in the Taihu Lake Basin from1985 to 2017 was 10847.41Gg,which showed a fluctuating downward trend.The emission intensity was basically in the range of 36-563kg/ha,and the average emission intensity was 185kg/ha.In terms of spatial distribution,the areas with relatively high values of CH4 emissions in each year are mainly concentrated in the area around the Taihu Lake(except the southwest),the southern and eastern areas of the Taihu Lake Basin.The regions with relatively low annual emissions are distributed in the northern and southeastern regions of the Taihu Lake Basin.(4)The dominant factors in the spatial distribution of CH4 emissions in the Taihu Lake Basin are soil clay content and soil bulk density.The content of soil clay particles is extremely negatively correlated with CH4 emissions(R=-0.85,P<0.01),and the soil bulk density is extremely significantly positively correlated with CH4 emissions(R=0.5,P<0.01).The main factors for the temporal changes of CH4 emissions in the Taihu Lake Basin are the amount of nitrogen fertilizer,the daily maximum temperature in the rice season,the minimum daily temperature in the rice season,and the average daily rainfall in the rice season.The amount of nitrogen fertilizer,the average daily minimum temperature of the rice season,and the average daily rainfall of the rice season are extremely negatively correlated with CH4 emissions(R=-0.24?-0.16?-0.14,P<0.01),and the average daily maximum temperature of the rice season is extremely significantly positively correlated with CH4 emissions(R=0.15,P<0.01).(5)Straw return to the field and reduced fertilization both stimulated CH4emissions from rice fields in the Taihu Lake Basin.Under the same fertilization scenario,the effects of different straw-returning models on CH4 emissions are as follows:rice straw-returning and non-wheat straw-returning>wheat straw-returning and non-rice straw-returning>all straw-returning>non-straw-returning;under the same straw return mode,the effects of different types of reduced fertilization methods on CH4emissions are as follows:reduced fertilization 40%>reduced fertilization 30%>reduced fertilization 20%>no reduced fertilization;(6)The impact of straw return is significantly greater than the impact of fertilization on CH4 emissions.Compared with the baseline scenario(non-straw-returning and non reduction in fertilization),rice straw-returning and non-wheat straw-returning,wheat straw-returning and non-rice straw-returning,all straw-returning increased CH4 emissions by 18.04%-21.12%,26.39%-32.14%,38.01%-42.01%respectively;reduced fertilization by 20%?30%and 40%increased CH4 emissions by0.19%-0.71%,0.39%-1.09%,and 0.51%-1.52%respectively.Considering only the element of CH4 emission reduction,it is recommended that the Taihu Lake Basin adopt non-straw-returning and non-reduction in fertilization. |
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