Effect Of Vegetation Restoration On Soil Carbon Storage In Southwest China

Vegetation restoration is an effective way to increase soil carbon?C?sequestration and C sequestration potential,and it is an important strategy to mitigate climate change.The karst landform is widely distributed in southwest,which is the most concentrated area in China.In addition,it has a steep and fragmentary landform pattern,leads to the ecological environment is fragile.Long term agricultural development leads to serious soil erosion and large area of bedrock exposed,which further aggravates the severity of rocky desertification.Karst region is a key area for vegetation restoration because of its great difficulty in ecological restoration.At present,the ecological restoration project has been implemented for more than 20 years in southwest China,and the assessment of its ecological benefits has become the focus of common concern of the academic community and society.Under the background of large-scale ecological engineering in Southwest China for many years,based on the synthetic analysis of historical documents,field sampling,remote sensing data set,soil database and meteorological database,this study analyzes the dynamic changes of soil C pool after vegetation restoration on a regional scale.This study focuses on the comparative study of karst and non-karst areas in southwest.Firstly,the similarities and differences of soil C change between the two areas are analyzed,and then the relationship between environmental factors is analyzed.Finally,the complex relationship between soil C pool change and environmental variables is quantitatively analyzed by structural equation model.The purpose is to clarify the direct and indirect factors that affect soil C pool after vegetation restoration,and to reveal the differences of soil C sequestration mechanism between karst and non-karst areas.This study is expected to provide a scientific basis for the formulation of emission reduction and exchange increase strategies in southwest China in the future.The main conclusions of this study are as follows:?1?The soil C storage showed an increasing trend after vegetation restoration in southwestern China,and the benefits of vegetation restoration for C sequestration were significant.Based on the analysis of time change,it is found that the years of vegetation restoration affect the change of soil C storage.In the early stage?1-3 years?of vegetation restoration,the soil C pool shows a decreasing trend.In the middle stage?4-18 years?,the rate of C sequestration keeps a steady growth.In the later stage,the rate of soil C sequestration slows down,and the soil C pool tends to be saturated.The results show that the growth of soil C storage has obvious lag.Based on the analysis of soil vertical profile,the C sequestration of different soil layers is quite different.Compared with other soil layers,the C sequestration rate in the surface layer of 0-10cm is more affected by vegetation restoration(0.45 Mg ha^-1 yr^-1).0-10 cm and 10-20cm soil C sequestration accounts for 24%and 16%of 0-100 cm soil C sequestration,respectively.Based on the analysis of vegetation types,C sequestration of natural secondary forest was the highest after vegetation restoration,followed by shrubs,grasses,and artificial forests were relatively low.For the entire southwestern region,soil C sequestration has a significant correlation with climatic factors.In the short term,mean annual temperature?MAT?is the main factor affecting soil C sequestration,and in the long term,it is mean annual precipitation?MAP?.In addition to climate factors,initial soil C storage is also related to soil C sequestration.?2?There are obvious differences in the evolution characteristics of soil C sequestration between karst and non-karst areas.The rapid increase of soil C storage in non-karst areas is mainly concentrated in the early stage of vegetation restoration,while karst areas have faster and more lasting C sequestration capacity.The surface soil C pool in Karst and non-karst areas increased significantly in the early stage of vegetation restoration,while the deep soil C pool had no significant change in the early stage.In the middle period of vegetation restoration,the change trend of C sequestration rate of soil layers in Karst and non-karst areas is different,and the trend of C sequestration in karst areas is on the rise,while that in non-karst areas is on the decline.In the later stage of vegetation restoration,the growth of soil C pool in karst area decreased significantly,while in non-karst area,it gradually became stable and had no significant change.The soil C sequestration efficiency in karst area is higher than that in non-karst area because of the limitation of different factors.The C storage of karst and non-karst soil profiles showed a similar trend:the rate of soil C sequestration decreased with the increase of soil depth.In the 0-100 cm soil layer,the rate of soil C sequestration in karst(6.17 Mg ha^-1 yr^-1)is about 31%higher than in non-karst areas(4.71 Mg ha^-1 yr^-1).The rate of soil C sequestration in karst areas is significantly higher than in non-karst areas in 13-18 years,and it is about 67.94%higher in the 0-100 soil layer,and there is no significant difference between the other years?1-6,7-12,?19 years?.The soil C sequestration in shrub-grasslands in karst areas is significantly higher than other vegetation types,and soil C sequestration in natural secondary forests and shrublands in non-karst areas is relatively high.The study has shown that in the past two decades,both karst and non-karst areas have obvious heating trends.Compared with that before vegetation restoration,the average temperature rise is about 0.48?.The interannual fluctuations of average precipitation obviously have no obvious change pattern.The average Gross Primary Productivity?GPP?and Net Primary Productivity?NPP?in karst areas are lower than those in non-karst areas.The average GPP is about 2.98%lower and the NPP is about 5.10%lower,and with no significant difference.?3?Topographical factors indirectly affect changes in soil C sequestration by affecting environment and soil properties.N and MAP are the main influencing factors of soil C sequestration in karst areas,while MAT and N are the main influencing factors in non-karst areas.The rate of C sequestration in karst soil is faster and more durable than in non-karst areas,which mainly corresponds to the climatic gradient in the southwest and the N content in the soil.MAP and P in karst areas can offset the negative impact of soil N sequestration on soil C sequestration,while soil C sequestration in non-karst areas appears as N-limitation.