Response Mechanism Of Soil Organic Carbon Storage To Land-use Change From Primary Forest

Soil is the most important and largest carbon pool on land in the world,about1550Pg.Land use change is the second largest source of man-made Greenhouse gas（GHG）emissions.The loss of Soil organic carbon（SOC）will result in the increase of CO₂emission after the primary forest is cut down or burned and converted to other land use types.However,there are few quantitative studies on the impact of land use type change on SOC in primary forest ecosystems,mainly because of the uneven data quality（some studies only reported SOC concentration without SOC storage;Some studies did not provide soil bulk density data;In some studies,soil sampling depth is shallow）and data are not representative enough.In this study,we conducted a meta-analysis of 1223 original data from 173 related literatures to estimate the change in SOC storage after the conversion of primary forest land use types to grassland,cropland,and secondary forest.On this basis,to explore how SOC reserves of different soil depth and climatic zone response,according to the research of soil samples,sampling depth and the experiment site climatic zone of the collected data compiled into different soil profile（0～20 cm,0～30 cm,more than 30 cm）and the different climatic zone and of the tropical,temperate,are analyzed.The results show that:（1）After the primary forest was converted into grassland,the overall SOC storage increased by 13.3%.In terms of soil profile,0～20cm increased by 11.9%.0～30cm increased by 11.3%;An increase of 6.4%over 30cm.From the climatic zone,the SOC reserves in the tropics increased by 7.7%.Temperate zones increased by24.7%.（2）After the primary forest was converted into cropland,the total SOC reserves decreased by 26.3%.Among them,from the soil profile,0～20cm decreased by 31.6%;0～30cm decreased by 28.2%;Over 30cm decreased by 10.1%.In the climate zone,SOC storage in the tropics decreased by 23.6%.Temperate zone decreased by 30.6%.（3）After the primary forest was converted into secondary forest,SOC storage decreased by 27.7%.Among them,from the soil profile,0～20cm decreased by 29.4%;0～30cm decreased by 26.8%;Decrease by 27.5%over 30cm.In the climate zone,SOC storage in tropical area decreased by 25.6%;Temperate zone decreased by29.7%.Regression analysis using the General Linear Model shows that:The total SOC increment decreased with the increase of Mean annual temperature（MAT）and Mean annual precipitation（MAP）（P<0.05）.The SOC increment in tropical and temperate zones was negative correlated with MAP（P<0.05）;Meanwhile,there was no significant correlation between MAT and SOC in tropical and temperate regions（P=0.1）.Multiple regression model analysis shows that MAT has interaction effect with climatic zone.MAT,MAP and climate zone interactive multiplication models could explain 41%of the variation.There was a significant positive correlation between MAP and SOC loss after the primary forest was converted into arable land（P<0.05）.However,there was no significant correlation between the absolute SOC loss and MAT and MAP after conversion to secondary forest（P=0.1）.