Study On The Impact Of Future Climate Change On Carbon Sequestration In Paddy Soil In Fujian Province

Clarifying the carbon’source/sink’’effect in cropland over China under future climate change is the basis for making reasonable carbon neutralization policies.Compared with dry land,paddy soil in China has great potential for carbon sequestration and is more sensitive to climate change.Based on this,this study takes the DNDC（De Nitrification and De Composition）model,which is widely used in farmland ecosystems,as an effective technical method,and selects paddy fields of Fujian Province,a typical subtropical region in China,as the study area,based on the data of 15 833 cultivated land fertility survey samples of the Ministry of Agriculture and Rural Affairs in 2016,the meteorological data from 1980 to 2016 and the agricultural management measures in 2016.The dynamic changes of soil organic carbon under different climate scenarios from 2017 to 2053 were simulated by using the 1:50 000 scale soil polygon as the minimum simulation unit,which fully reflects the spatial heterogeneity of soil properties.The dynamic changes of soil organic carbon under temperature,CO₂concentration and rainfall in the whole study area,different paddy soil subgroups and administrative regions were systematically analyzed,and the quantitative relationship between future climate change and soil carbon"source/sink"was clarified.The results can provide a theoretical basis for formulating reasonable carbon neutralization management measures in subtropical regions of China under the background of future climate change.The main research results are as follows:1.From the verification results of 6880 paddy field samples in 2016,100%of the soil organic carbon simulation values are within the range of measured point content,and the simulation results are in good agreement with the measured values.In addition,the correlation coefficient between simulated and measured values of soil organic carbon was 0.41,which reached a very significant correlation level（p<0.01）.The absolute value of relative error E is 8.18%,which meets the feasibility standard of model simulation results.The root mean square error（RMSE）and mean absolute error（MAE）were 5.46 g kg^-1and 4.31 g kg^-1,respectively,which were also small,indicating that the DNDC model could be applied to the simulation of paddy soil organic carbon in Fujian Province.2.Under the conventional scenario,the total soil organic carbon fixation in 37 years was 11.56 Tg C,and the average annual carbon fixation rate was 173 kg C hm^-2a^-1.In terms of soil types,two paddy soil subclasses,percogenic paddy soil and hydromorphic paddy soil,contributed most to the"source/sink"of paddy soil in Fujian Province,accounting for about 82%of the total carbon sequestration of paddy soil in the province.The highest annual carbon sequestration rates of salinized paddy soil and acid sulfate paddy soil were 249 and 220 kg C hm^-2a^-1,respectively.As for different administrative regions,Quanzhou and Zhangzhou had the largest contribution rate to paddy soil’carbon sink’’in Fujian Province,and their total carbon sequestration accounts for about36%of the total carbon sequestration of paddy soil in Fujian Province.The highest annual carbon sequestration rates in Putian and Quanzhou were 267 and 246 kg C hm^-2a^-1,respectively.3.With the increase of future temperature,the organic carbon sequestration rate of paddy soil in Fujian Province decreased significantly.Compared with the conventional treatment,the total carbon sequestration of paddy soil in Fujian Province from 2017 to 2053 decreased by 2.12,4.48 and 6.65 Tg C,respectively,by 18%～58%under three scenarios of temperature rise of 2°C,4°C and 6°C.In terms of different soil types,gley paddy soil was most affected by the increase of temperature,and the decrease of carbon sequestration rate was between 20%～69%under different treatments;however,saline paddy soil was least affected with the carbon sequestration decrease rate between 14%～43%.As for different administrative regions,Sanming city,which is located near the Wuyi Mountains,was the most affected by the increase of temperature,whose rate of carbon sequestration decreases between 27%～83%under different treatments;however,the coastal cities such as Quanzhou and Putian were the least affected with the carbon sequestration decrease rates between 10%～41%and 14%～42%,respectively.4.The change of rainfall has little effect on soil organic carbon,and as rainfall increases,soil organic carbon sequestration increases.Compared with the conventional treatment,the amount of carbon sequestration increased by 0.06 Tg C and carbon sequestration rate increased 0.56%with an increase of 20%in rainfall;however,under the scenario of 20%rainfall reduction,compared with the conventional treatment,soil organic carbon sequestration decreased by 0.08 Tg C and carbon sequestration rate decreased by 0.7%.In terms of different soil types,the acid sulfate paddy soil was the most affected by the reduction in rainfall,which was 1.79%lower than the conventional carbon sequestration rate,and the submergenic paddy soil was the least affected by the reduction in rainfall,which increased by 0.66%over the conventional carbon sequestration rate.The increase of rainfall by 20%had the greatest impact on the carbon sequestration rate of the gleyed paddy soil,while the carbon sequestration rate of the hydromorphic paddy soil had the smallest impact.Compared with the conventional treatment,the two increased by 3.1%and 0.21%,respectively.From the perspective of different administrative regions,the 20%reduction in rainfall had the greatest impact on the carbon sequestration rate in Putian City,an increase of 1.79%over the conventional carbon sequestration rate,while the impact on Sanming City was the smallest,which was0.32%lower than the conventional carbon sequestration rate.The 20%increase in rainfall had the greatest impact on the carbon sequestration rate in Nanping City,while the impact on the carbon sequestration rate in Zhangzhou City was the smallest,an increase of 2.98%and 0.14%respectively compared with conventional treatment.5.Elevated CO₂concentration is beneficial to the fixation of paddy soil organic carbon in Fujian.Compared with the conventional treatment,the total carbon sequestration of paddy soil in Fujian Province increased by 0.27,0.52 and 1.02 Tg C,respectively,with an increase of 3%～9%,when the CO₂concentration increased by 0.5,1 and 2 times.From the perspective of different soil types,salinized paddy soil was the least affected by elevated CO₂concentration,and the increase was between 2%and 7%compared with conventional treatment.However,the increase of CO₂concentration had the greatest impact on the gleyed paddy soil,which increased by 5%～13%compared with the conventional treatment.From the perspective of different administrative regions,under the scenario of CO₂concentration,compared with conventional treatment,Sanming City and Nanping City in the northwest region had the largest increase in carbon sequestration rate,between 5%～14%and 4%～13%,respectively,relatively speaking,the increase in CO₂concentration had less impact on Ningde City and Quanzhou City,and compared with conventional treatment,the increase in carbon sequestration rate was between 2%～9%and 2%～7%,respectively.6.The total carbon sequestration of paddy fields in Fujian Province were 10.22,7.14,5.42,9.28,6.95 and 4.80 Tg C under T₂I₂（Temperature rise 2°C and rainfall increase 20%）,T₄I₂（Temperature rise 4°C and rainfall increase 20%）,T₆I₂（Temperature rise 6°C and rainfall increase20%）,T₂D₂（Temperature rise 2°C and rainfall decrease 20%）,T₄D₂（Temperature rise 4°C and rainfall decrease 20%）,T₆D₂（Temperature rise6°C and rainfall decrease 20%）,respectively;The annual average carbon sequestration rates were:153,107,81,139,104 and 72 kg C hm^-2,respectively,Compared with the conventional treatment,the reduction rates were 12%,38%,53%,20%,40%and 59%,respectively.The results showed that compared with the conventional treatment,the carbon sequestration rate was decreased under the interaction of temperature and rainfall,but the overall effect was still"carbon sink".The effect of the interaction of rainfall reduction and temperature increase on soil carbon sequestration rate was generally greater than that of rainfall increase and temperature increase.7.Grey correlation analysis showed that initial organic carbon,clay,bulk density and p H had great influence on the average annual carbon sequestration rate,while annual temperature,rainfall and slope had little influence on the average annual carbon sequestration rate.Multiple linear stepwise regression showed that the initial organic carbon and clay had a greater explanation for the change of annual carbon sequestration rate under different climate scenarios,ranging from 35.4%～43.1%and18.4%～23%,respectively.The explanation of bulk density and p H for the change of annual carbon sequestration rate under different climate scenarios was small,ranging from 0.2%to 0.3%.