Soil Organic Carbon Characteristics And Carbon Sink Function Evaluationat Different Vegetation Restoration Stages In Karst Plateau Region

Global climate change,drawing much attention all over the world,which is also a hot issue in modern ecology research.The Chinese government aims that by 2030,carbon dioxide emissions will no longer increase after reaching the peak,and by 2060,the total amount of greenhouse gas emissions be off set by afforestation,energy conservation and emission reduction.As soil carbon sink has great potential and cost advantage in carbon emission reduction,and its dynamic change is an important factor affecting the global carbon cycle.Therefore,it's quite important to make clear how to increase the accumulation and stability of soil organic carbon so as to promote the conversion and storage of atmospheric carbon dioxide into soil in the global climate change research.In this article,through replacing time with space,the herbaceous community stage-shrub stage-arbor stage-climax stage as a succession climax stage of karst plateau is selected as the main research object.In the 42 fix standard samples set up in vegetation restoration stage,by means of field investigation and indoor experiment,the author led a research on the changes in characteristics of soil organic carbon.The existing soil carbon saturation model was used to estimate the soil carbon sequestration potential in the vegetation restoration stage and to quantify the soil carbon sequestration capacity in the vegetation restoration process.Besides,taking Guiyang city as an example,the author has made a preliminary assessment of the present and potential value of soil carbon sequestration of different vegetation types through accounting method-“ecocoin”,namely,calculating the amount of ecological resources in ecocoin,to improve the ecological metadata database in Guiyang with forest soil carbon sequestration value of ecological metadata database.The main conclusions are as follows:(1)Soil organic carbon content(SOCC)and organic carbon density(SOCD)increased with vegetation restoration.In the process of vegetation restoration,the SOC content in 0?30cm soil layer varied from 20.97?40.67 g·kg^-1in the herbaceous stage,with an average of 29.27 g·kg^-1.The shrub stage was 30.36?88.31 g·kg^-1with an average of 56.95 g·kg^-1,the arboreal stage was 26.86?59.81 g·kg^-1with an average of 41.27 g·kg^-1,and the peak stage was 34.17?102.35 g·kg^-1with an average of 65.33g·kg^-1.The organic carbon density(SOCD)varied from 2.00 kg·m^-2to 3.56 kg·m^-2with an average of 8.02 kg·m^-2at herbaceous stage,from 2.30 kg·m^-2to 5.45 kg·m^-2with an average of 11.14 kg·m^-2at shrub stage,from 2.34 kg·m^-2to 4.61kg·m^-2at arboreal stage,and from 2.73 kg·m^-2to 7.03 kg·m^-2at peak stage with an average of13.83kg·m^-2.SOCC and SOCD increased by 123.20%and 72.44%from the herbaceous stage to the climax stage.With the natural restoration of vegetation,the soil organic carbon pool was basically improved.(2)The distribution rule of SOCC and SOCD in soil profile was as follows:SOCC and SOCD in surface soil were significantly higher than those in deep soil,that is,with the increase of soil depth,both SOCC and SOCD showed a downward trend,and the distribution of soil organic carbon showed a phenomenon of“surface aggregation”.The specific distribution characteristics were as follows:the SOCC in the 0?10cm soil layer was 40.67?102.34 g·kg^-1,with an average value of 72.78 g·kg^-1;SOCC in the 10?20cm soil layer was 26.18?59.48 g·kg^-1,with an average of 43.75g·kg^-1.SOCC in the 20?30cm soil layer was 20.97?34.17 g·kg^-1,with an average value of 28.09 g·kg^-1.SOCC in the 0-10cm soil layer was 1.66 times and 2.59 times of that in the 10?20cm and 20-30cm soil layers,respectively.SOCD in the 0?10cm soil layer was 3.56?7.03 kg·m^-2,with an average of 5.16 kg·m^-2and 2.45?4.07kg·m^-2in the 10?20cm soil layer;SOCD in the 20?30cm soil layer was 2.00?2.73kg·m^-2,with an average of 2.34 kg·m^-2.SOCD in the 0-10cm soil layer was 1.59 times and 2.21 times of that in the 10?20cm and 20?30cm soil layers,respectively.(3)With the change of vegetation restoration,SOCC and SOCD are affected by many vegetation and soil factors.This study shows that in the process of vegetation restoration,the physical and chemical properties of vegetation and soil are important factors affecting the change of soil organic carbon pool.SOCC was negatively correlated with litter C/N and soil bulk density(p<0.01),and positively correlated with litter TN,N/P,soil TN,C/P,N/P(p<0.01).SOCD was negatively correlated with litter TP(p<0.01),positively correlated with litter N/P,soil C/P and bulk density(p<0.01),and positively correlated with soil TN and N/P(p<0.05),indicating that the changes of SOCC and SOCD with vegetation restoration were affected by vegetation factors and soil factors.According to principal component analysis,SOCC and SOCD were closely related to community biomass,root biomass,litter TC,TP,C/P,N/P,soil gravel content,TN,C/N,C/P and N/P.Step-up regression analysis showed that TP,C/P and TN,C/N and C/P had significant effects on SOCC.The regression model was as follows:SOCC=11.56 soil TN+0.56 soil C/N-10.46 soil C/P+0.667 litter TP+4.824(R=0.960,p<0.01).Soil TP and C/P had significant effects on SOCD,and the regression model was as follows:0.11 litter TP+2.434(R=0.673,p<0.01).Therefore,in the process of vegetation restoration,litter TP,C/P,soil TN,C/N,C/P are the important factors affecting the change of soil organic carbon pool.(4)In the process of restoration of degraded karst vegetation,the CPOC of herbage,shrub,arboreal and terminal stages were 19.70,30.03,24.84,29.34 g·kg^-1,FPOC of 6.43,12.75,9.82,22.90 g·kg^-1,and MOC of 3.15,6.60,4.80,10.65 g·kg^-1,respectively.Soil organic carbon content of each component increased with the vegetation restoration process,but had a low value in the arbor stage,that is Climax stage>shrub stage>arbor stage>herbaceous community stage.Coarse organic carbon(CPOC)increased by 49%,fine organic carbon(FPOC)increased by 2.56times,and MOC increased by 2.38 times from herbaceous stage to climax stage.In the soil profile,the carbon content of soil components decreased with the increase of soil depth.In the process of vegetation restoration,the CPOC of 0?10cm ranged from30.09?56.02 g·kg^-1to 18.35?30.30 g·kg^-1for 10?20cm and 10.65?14.25 g·kg^-1for20?30cm,and the significance of the difference of carbon content of each component also decreased with the increase of soil depth.In each stage of vegetation restoration,CPOC accounted for the highest proportion,followed by FPOC and MOC.With the increase of soil depth and vegetation restoration,the proportion of CPOC decreased,while the proportion of FPOC and MOC increased.POC/MOC decreased with vegetation restoration,and decreased significantly with soil depth increasing.Comprehensive,this study of soil carbon sequestration ability and stability of organic carbon in the climax stage,herbaceous community lowest,deep soil organic carbon is surface soil organic carbon stability strong,vegetation restoration,soil depth has a promoting effect on the stability of soil organic carbon,each karst vegetation soil organic carbon are mainly composed of coarse particle organic carbon,shows that karst plateau vegetation soil carbon sequestration ability and organic carbon less stable,relatively weak and vulnerable to interference caused by soil organic carbon loss.(5)The soil carbon saturation capacity(CSC)of 0?10cm,10?20cm and20?30cm soil layers in the peak stage of karst plateau region was 23.08 g·kg^-1,27.93g·kg^-1and 31.22g·kg^-1,respectively,and the average value of soil CSC of 0?30cm profile was 27.41 g·kg^-1.Soil carbon sequestration potential(CSP)increased with soil depth.At each stage of vegetation restoration,CSP had significant differences among soil layers(p<0.05),and CSP increased with the increase of soil depth.Between different vegetation recovery phase,the average CSP is herbaceous community stage(5.34 kg·m^-2)>long boled stand stage(5.04 kg·m^-2)>shrub stage(4.73kg·m^-2)>climax stage(3.85 kg·m^-2),and the results show that vegetation restoration in the early stages,deep soil carbon saturation deficit(CSD)is larger,lower carbon saturation level(CSL),shows that vegetation restoration can increase the stability of the accumulation of organic carbon in soil,and the deep soil with large carbon sequestration potential.(6)The SOCC,SOCD and CSP of different plant communities were different in the same vegetation restoration stage.According to the soil profile analysis of 0-30cm,the variation coefficients of SOCC,SOCD and CSP at each vegetation restoration stage were 32%,30%and 5%at the herbaceous stage,28%,22%and 4%at the shrub stage,52%,36%and 13%at the arboreal stage,and 9%,7%and 13%at the climax stage,respectively.In conclusion,the soil organic carbon in the arbor stage community varies greatly due to the diversity of single or complex forest type and coniferous or broad-leaved plant species.Therefore,when calculating the guiyang city vegetation soil organic carbon reserves,to classify the vegetation types can be divided into grass,shrub and coniferous forest,mixed needle leaf,deciduous broad-leaved forest,evergreen broad-leaved forest and evergreen and deciduous broad-leaved mixed forest soil,7 vegetation types are climax stage in evergreen and deciduous broad-leaved forest,by area,add and calculated.(7)The SOCD of herbaceous community,shrub community,coniferous forest,coniferous and broad-leaved mixed forest,deciduous broad-leaved forest,evergreen broad-leaved forest and evergreen and deciduous broad-leaved mixed forest were 7.91,10.85,7.88,6.94,10.05,7.93,16.62kg·m^-2.CSP was 5.34,4.73,5.78,5.36,5.21,5.18,3.74kg·m^-2.The variation of SOCD in 7 different community types was evergreen and deciduous broad-leaved mixed forest>shrub community>evergreen broad-leaved forest>coniferous forest>herbaceous community>deciduous broad-leaved forest>coniferous and broad-leaved mixed forest,and the variation range was22.93-81.73g·kg^-1and 6.94?16.62kg·m^-2,respectively.The variation of CSP among community types was opposite to that of SOCD,and the variation range was3.74?5.79kg·m^-2.(8)Soil carbon sequestration and carbon sequestration potential value in different vegetation community types calculated based on the above community types soil SOCD,CSP,calculated based on the karst plateau herb community,shrub community,coniferous forest,mixed needle leaf,deciduous broad-leaved forest,evergreen broad-leaved forest and evergreen and deciduous broad-leaved mixed forest soil current carbon sink value per unit area were 30.31,42.10,29.77,26.22,37.97,29.98,62.84 eco-coin/m²,carbon sequestration potential value were 20.18,17.89,21.88,20.25,19.68,19.57,14.13 eco-coin/m²,vegetation community types soil average current carbon sink,carbon sequestration potential value were 37.03,9.08eco-coin/m²,the changing rule of the current value of carbon sequestration is Evergreen and deciduous broad-leaved mixed forest>shrub community>evergreen broad-leaved forest>herbaceous community>deciduous broad-leaved forest>coniferous forest>coniferous and broad-leaved mixed forest.Its variation range was26.22-62.84 eco-coin/m²;On the contrary,the variation of potential carbon sink value ranged from 14.13 to 21.88 eco-coin/m².(9)The total current soil carbon storage is about 38 million t,and the potential carbon storage is about 19 million t.The current carbon sink value of vegetation soil in Guiyang is 147.575 billion eco-coin,and the potential carbon sink value is 73.54billion eco-coin.