| Fencing for grazing exclusion is a common land-use method in the semi-arid areas of the Loess Plateau in China,which have been widely found to change grassland soil organic carbon(SOC),but the empirical studies that evaluated driving factors of soil carbon(C)stocks under the different land use are still weak.This study investigated the Typical Steppe on the Loess Plateau,China.Four natural grasslands with different enclosure years(GG,FG10,FG15 and FG30 years)were selected.The dynamic changes and distribution characteristics of carbon stock in deep soil(0?200cm)under different enclosure years were compared and analyzed,and the change process of soil carbon sink in the process of ecosystem restoration and reconstruction was studied.In addition,grazing grassland and fenced grassland for 8 years were selected,we investigated the soil C stock variations and the main driving mechanism of soil C accumulation in the surface layer(0?30 cm);clarified the dynamic characteristics of the carbon sequestration in the process of ecological restoration and reconstruction.These have important reference value for scientific evaluation to carbon sequestration effect of the soil in the process of vegetation restoration environment.The main results are as follows:(1)Soil carbon stock in 0?200 cm soil layer increased with increase in years of fencing.Soil carbon sequestration was 193.27 Mg ha-1 after 30 years of vegetation restoration.Soil carbon sequestration in 0?20 and 20?40 cm soil layers was 32.79 and 33.54 Mg ha-1,accounting for 16.96%and 17.35%of total carbon sequestration in 0?200 cm soil layer,respectively.The average soil carbon sequestration rate was 6.44 Mg ha-1 yr-1 in 0?200 cm soil layer,and 1.09 and 1.12 Mg ha-1 yr-1 in 0?20 and 20?40 cm soil layers,respectively.In the process of grassland vegetation restoration,the soil carbon sequestration rate in 0?100 cm soil layer decreased and then increased,while that in 100?200 cm soil layer increased first and then decreased,and the soil carbon sequestration rate in 20?40 cm soil layer was the highest after 10 years of grassland vegetation restoration.(2)There was a significant positive correlation between soil carbon stock and soil nutrient content through the long-term restoration succession.Soil C/N in 0?120cm soil layer showed an increasing trend,and reached the maximum in 30 years of vegetation restoration,The C/N ratio of 120?200 cm soil layer reached the maximum in 15 years.Restoration age and soil C/N were the main factors affecting soil carbon stock,and soil depth significantly affected the vertical distribution of soil carbon stock.The carbon stock in deep soil(100?200 cm)has a more significant dynamic change,which is due to the continuous carbon sink in surface soil during vegetation restoration.(3)The soil C stock in the top soil layer(0-10 cm)of fenced grassland was significantly higher than that of grazed grassland.Fencing increased the SOC,total nitrogen(TN)and C/N ratio,and significantly increased the aboveground biomass(AGB),belowground biomass(BGB),and the amount of soil large macro-aggregates in the top soil layer(0-10 cm),and the soil stability was improved.The bulk density(BD),soil moisture content(MC),and soil porosity(SP)had no significant difference between fenced and grazed grassland.Meanwhile,grazing increased soil temperature(ST)and soil respiration(Rs).The soil C/N ratio,BD,and TN are the important factors affecting soil carbon stocks.However,the main controlling factors of different land use are different.The soil carbon storage of the FG is mainly affected by C/N and MC;while the soil carbon stock of the GG is mainly affected by BD,C/N and TN. |
PDF Full Text Request