Study On The Distribution Characteristics Of Soil Organic Carbon And Its Influencing Factors Following Afforestation

Global warming and elevated atmospheric carbon dioxide concentrations are slowly affecting the structure and function of global terrestrial ecosystems,threatening human survival and development.Afforestation is an important measure to cope with global changes,having great significance in enhancing terrestrial carbon sinks,reducing soil erosion,and mitigating global warming.Afforestation mediates regional carbon balance and climate change by impacting changes of soil carbon pools,and plays an important role in terrestrial ecosystems.The change of soil organic carbon in afforestation is also one of the important contents to evaluate vegetation restoration measures and their ecological benefits.This paper in order to understand the distribution of soil organic carbon after afforestation in the Yangtze River Basin and explore the influencing factors of soil organic carbon nationwide,through the field investigations with a total of 1395 soil samples to analyze the distribution characteristics of soil organic carbon following afforestation in the Yangtze River Basin,and combined with the literature information collected with a total of 430 sample points to comprehensively analyze the influencing factors of soil organic carbon on a nationwide scale.The main conclusions are as follows:(1)The soil organic carbon content of the afforestation land in the Yangtze River Basin gradually decreases with the increase of soil depth.Starting from the top soil to 60 cm,the average content of soil organic carbon decreases by 36.84% and 27.39% for every 20 cm of soil depth.Soil organic carbon mainly accumulates in the surface layer of 0-20 cm,accounting for 47.84% of the organic carbon content in the soil profile of 60 cm depth,and the proportions of 20-40 cm and 40-60 cm depth are 30.22% and 21.94%,respectively.It shows that the soil surface layer has a large carbon pool,so we should pay attention to the surface soil disturbance and the impact of land management on soil carbon.The coefficient of variation of the organic carbon content between each soil layer does not change much,ranging from 73.50% to 86.35%.It showed a moderate degree of variability.Compared with other regions,Guizhou,Yunnan,and Chongqing showed large coefficients of variation.In the microtopography sample 10m×10m,the soil organic carbon content of the downslope position was significantly greater than that of the middle and uphill positions(P<0.05),while there was no significant difference in organic carbon content between middle and uphill position(P>0.05).(2)With the increase of soil depth,the difference in soil organic carbon storage in different regions is decreasing.The northeastern and southwest regions show higher soil organic carbon storage,and the northwest region has lower soil organic carbon storage.Both mean annual precipitation(MAP)and mean annual temperature(MAT)have a significant impact on soil organic carbon.It shows that where the precipitation is less than 1200 mm,precipitation may be one of the factors that limit the accumulation of soil organic carbon.Deep soils with an MAT<5°C have a large carbon storage potential.Arbor forests have higher soil organic carbon storage,which is significantly higher than grasslands and shrubs(P>0.05).Soil organic carbon storage increases with the growth of vegetation restoration years,and the cumulative rates of soil organic carbon in soil layers 0-20 cm,20-40 cm,40-60 cm with the restoration period are 0.40 Mg/(ha·yr),0.26 Mg/(ha·yr)and 0.20 Mg/(ha·yr).The soil organic carbon storage generally increases first and then decreases with the change of slope,which is lower at slopes of 0-5° and>20°.Organic carbon storage has significant differences between different altitudes,zonal distribution with altitude.(3)In the surface soil,there are significant correlations between each environmental impact factor and soil organic carbon storage at the 0.05 level.MAT,MAP,vegetation restoration years,and altitude all have a significant positive correlation with soil organic carbon storage,and slope has a significant negative correlation.Overall,the storage of soil organic carbon in the 0-60 cm soil layer is significantly correlated with MAP,MAT,vegetation restoration years and altitude(P<0.01).Each environmental impact factor has a significant impact on soil organic carbon,and the interaction of precipitation and slope,temperature and altitude also has a very significant effect on soil organic carbon(P<0.01).The results of principal component analysis show that MAT,MAP,altitude,slope and vegetation restoration years are the main factors affecting soil organic carbon,the cumulative contribution rate is 66.401%.