| Fujian Province is a typical subtropical region in China,and its paddy field area accounts for more than 80%of the cultivated land area.Clearing the quantitative relationship between agricultural management measures and soil"carbon sink"is an important basis for rational formulation of China’s carbon neutrality national strategy.Based on this,this study takes DNDC（De Nitrification and De Composition）model,which is widely used in farmland ecosystem,as a tool,and selects paddy fields in 84 counties（cities and districts）in typical subtropical regions of China–the whole Fujian Province as the research area,Based on the data of 15,833 cultivated land fertility survey samples of the Ministry of Agriculture and Rural Affairs in 2016,meteorological data from 1980 to2016 and agricultural management measures in 2016,the improved1:50,000 large-scale soil map"Polygon",which fully reflects the spatial heterogeneity of soil attributes,was adopted as the minimum simulation unit.The dynamic change of soil organic carbon under different agricultural management measures was simulated from 2017 to 2053,and the change rule of soil organic carbon under different agricultural management measures was systematically analyzed in the whole study area,each paddy soil subcategory and administrative region,to clarify the quantitative relationship between agricultural management measures and soil carbon sink.The results can provide a theoretical basis for developing effective agricultural management measures for carbon sequestration and emission reduction in subtropical region of China.The main conclusions are as follows:1.The verification of the measured samples from a large sample showed that the measured values of 6880 organic carbon samples in 2016were significantly correlated with the simulated values（P<0.01）,the correlation coefficient was 0.41,and the relative error E was-8.18%.the mean absolute error（MAE）and root mean square error（RMSE）were4.31 g·kg-1and 5.46 g·kg-1,respectively,which indicated that the DNDC model could be used to simulate the dynamic changes of paddy soil organic carbon in Fujian Province.2.The increase of straw returning significantly increased the soil organic carbon content of paddy fields in Fujian province from 2017 to2053.Compared with traditional management（15%）,the average annual carbon sequestration rates of paddy soils under 30%,50%and 90%straw returning increased by 129,305 and 665 kg·hm-2,and the total carbon sequestration increased by 8.59,20.34 and 44.39 Tg,respectively,with an increase of 74%,176%and 384%.Among the sub-types of paddy soils,Percogenic paddy soil and Hydromorphic paddy soil contributed the most to the carbon sink of paddy fields in the province,more than 80%.In terms of different administrative regions,From the perspective of different administrative regions,about 45%of the carbon sink contribution of paddy soil in the province comes from Longyan,Quanzhou and Zhangzhou.3.Under no-tillage treatment,the average annual carbon sequestration rate in Fujian Province increased by 87 kg·hm-2compared with the traditional management,and the total carbon sequestration increased by 5.77 Tg,with an increase of 41.69%.Among the sub-types of paddy soil,the average annual carbon sequestration rates of Acid sulfate paddy soil and Salinized paddy soil under no-tillage were the highest,which were 333 and 337 kg·hm-2,respectively.82%of the contribution of carbon sink in paddy fields in the whole province came from Percogenic paddy soil and Hydromorphic paddy soil.From the perspective of different administrative regions,the carbon sequestration of Longyan,Quanzhou and Zhangzhou under no-tillage treatment was the largest,accounting for 8.20 Tg,accounting for 47.3%of the total carbon sequestration in the province.4.The soil organic carbon content in paddy fields of Fujian Province was significantly reduced without and with reduced nitrogen application（0.5 times of traditional management）,and the average annual carbon sequestration rates were 91.43%and 24.16%lower than those of traditional management,respectively.In contrast,when the application rate of nitrogen fertilizer was 1.5 and 2.0 times that of traditional management,the carbon sequestration potential was about1.07 and 1.09 times that of traditional management,respectively.From the perspective of each soil subclass,the"carbon source"effect was observed in the Gleyed paddy soil without nitrogen fertilizer.The carbon release rate wasis 16 kg·hm-2·a-1,and the carbon release wasis 0.12 Tg.The average annual carbon sequestration rates of Acid sulfate paddy soil and Salinized paddy soil were the highest under the application of nitrogen fertilizer（0.5,1.5 and 2.0 times of traditional management）,ranging from180 to 259 kg·hm-2,while the contribution of"carbon sink"of infiltrated paddy soil wasis the largest,more than 50%.From the perspective of different prefecture-level cities,Nanping,Ningde and Sanming showed a"carbon source"effect without nitrogen fertilizer.The average annual organic carbon release rate was between 19～58 kg·hm-2,and the total carbon release is 1.29 Tg.When nitrogen fertilizer was applied（nitrogen fertilizer was 0.5,1.5 and 2.0 times that of traditional management）,Quanzhou and Zhangzhou contributed greatly to the"carbon sink"of paddy soil in the whole province,and the total carbon sequestration accounted for about 35%of the total carbon sequestration in the whole province.5.When the application rate of organic fertilizer increased to 2,3and 4 times of the traditional management,the total amount of soil carbon sequestration were 19.69,27.84 and 35.70 Tg,respectively,and the carbon sequestration rates were 295,417 and 535 kg·hm-2·a-1,respectively,which were 1.7,2.4 and 3.1 times of the traditional management level.The average annual carbon sequestration rate of Acid sulfate paddy soil and Salinized paddy soil ranged from 220 to 666kg·hm-2and 249 to 749 kg·hm-2,respectively.The average annual carbon sequestration rate of Percogenic paddy soil and Hydromorphic paddy soil ranged from 9.45 to 29.30 Tg,accounting for 82%of the total carbon sequestration in the study area.In terms of administrative regions,longyan,Quanzhou and Zhangzhou contributed about 50%of the carbon sink of paddy soil under organic fertilizer treatment.6.The partial least squares regression analysis showed that the contribution degree（VIP value）of each influencing factor to the change of annual carbon sequestration rate was:initial organic carbon>bulk density>clay>organic fertilizer>rainfall>temperature>nitrogen fertilizer>p H.Further multiple linear stepwise regression analysis showed that the initial organic carbon and clay had the highest explanatory power for the annual average organic carbon change of different agricultural management measures,which were between7.3～39.8%and 17.3～30.5%,respectively,while bulk density and p H only explained 0.1～0.9%of the annual average organic carbon change（p<0.001）.Therefore,the initial organic carbon and clay particles are the main controlling factors affecting the annual average carbon sequestration rate of paddy soil in Fujian Province in the future.In the future,when simulating and predicting the soil carbon sequestration potential in Fujian Province or subtropical regions,the accuracy of parameter values（initial organic carbon and clay particles）should be ensured first. |
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