Different Characteriest Study Of Soil Carbon Fractions Of Artificial Vegetation Restoration In The Semi-arid Loess Plateau Of China

Under the policy background of returning farmland to forests and grassland,the purpose of this study was to compared the difference of soil carbon compsition among different artificial forests and between artificial pure forests and mixed forest.The experiment was conducted in Longtan catchment in Dingxi city,Gansu province,China.Seven sample sites include Populus tomentosa forest,Populus tomentosa + 5-years-old Pinus tabulaeformis mixed forest,Populus tomentosa + 10-years-old Pinus tabulaeformis mixed forest,Pinus tabulaeformis forest,Prunus armeniaca + Picea asperata mixed forests,Prunus armeniaca +Pinus sylvestris forest,Prunus armeniaca forest were chosen for this study.Soil total carbon,soil organic carbon,soil inorganic carbon,soil light fraction organic carbon and soil heavy fraction organic carbon were measured.Meanwhile,the main soil driving factors were measured.The main results were as follows:(1)The soil organic carbon content of different restored tree species was similar to that of the recombinant components.There were differences between the upper layer(0-40cm)and the lower layer(40-100 cm),0-40 cm soil layer,soil organic carbon of Populus tomentosa forest and the content of recombinant components was the lowest,and that of Prunus armeniaca forest was the highest;40-100 cm soil layer,the content of soil organic carbon and its recombinant components was the lowest,and the highest was Populus tomentosa forest.In the 0-40 cm soil layer,the soil organic carbon content of the Populus tomentosa forest was lower than that of the Prunus armeniaca forest and Pinus tabulaeformis forest,40-100 cm soil layer,and there was no significant difference in soil organic carbon in the three forest soils.The soil inorganic carbon content in the 0-10 cm soil layer of the Populus tomentosaforest,Prunus armeniaca forest and Pinus tabulaeformis forest was lower than that of other soil layers,and the decalcification phenomenon was obvious.In the underground of different degraded pure forests,the average carbon content of the soil from high to low was Prunus armeniaca forest>Pinus tabulaeformis forest>Populus tomentosa forest.The difference of soil total carbon content was mainly reflected in the upper layer of soil(0-20cm).(2)After the adjustment of vegetation community structure in degraded forest land,the changes of soil organic carbon in mixed forests were similar to those in single pure forest,and they have different degrees of improvement,while the soil heavy organic carbon and light organic carbon vary under different mixed forests.Compared with the Prunus armeniaca forest,the soil light and heavy group organic carbon of the Prunus armeniaca + Pinus sylvestris forest were increased,while the soil light organic carbon content of the Prunus armeniaca + Picea asperata mixed forests decreased.In the soil of Populus tomentosa +Pinus tabulaeformis mixed forest,the light organic carbon increased first and then decreased,while the heavy organic carbon continued to increase.The increase of organic carbon was mainly from heavy organic carbon.After the single pure forest was adjusted to mixed forest,the decalcification of surface inorganic carbon still existed,but the calcium accumulation layer moved up to the surface and the soil inorganic carbon content of the mixed forest calcium layer was higher than that of pure forest.The soil carbon content of mixed forest land was higher than that of single pure forest.After adjusting the community structure of degraded forest land to form mixed forest,soil organic carbon and its heavy components,soil inorganic carbon and soil total carbon increased with the increase of vegetation restoration years.The structural change of different species adjusted to mixed forests in a single degraded forest land can increase the carbon sequestration potential of the soil.(3)Compared with Populus tomentosa forest,Prunus armeniaca forest and Pinus tabulaeformis forest,Pinus tabulaeformis forest had the best soil carbon sequestration effect and Populus tomentosa forest was the worst.After the community structure of degraded pure forest was adjusted to mixed forest,the soil organic carbon,inorganic carbon and total carbon storage increased in varying degrees.After the degraded Populus tomentosa forest was adjusted to Populus tomentosa + Pinus tabulaeformis mixed forest,the soil organic carbon storage and total carbon storage of mixed forest increased with the increase of vegetation restoration years,and the structure adjustment mode of mixed forest could improve the soil carbon sequestration capacity.(4)Pearson correlation analysis showed that soil total carbon content was significantly positively correlated with soil organic carbon,soil organic carbon,soil moisture,soil total nitrogen,fine root biomass,microbial biomass carbon and microbial biomass nitrogen,and soil inorganic carbon.There was a significant positive correlation between the content andsoil recombination carbon content,and a significant negative correlation with soil bulk density and soil pH.Soil organic carbon content was significantly positively correlated with soil light weight,recombinant organic carbon,soil moisture,soil total nitrogen content,fine root biomass,microbial biomass carbon and microbial biomass nitrogen,and was significantly negative with soil bulk density and soil pH.Correlation,the correlation with other indicators was not obvious.Soil inorganic carbon had a significantly negative correlation with microbial biomass carbon and microbial biomass nitrogen.The path analysis results show that the effect of soil total nitrogen content on soil organic carbon was the direct effect in the restoration process of artificial forest vegetation in Longtan catchment of Loess Plateau,and it was the dominant factor acting on soil organic carbon.The effects of soil microbial biomass carbon and soil pH on soil organic carbon was mainly indirect effects.Soil microbial biomass carbon had a positive effect on soil organic carbon and soil pH had a negative effect.The three driving factors collectively dominate the changes in soil organic carbon content.The correlation between soil driving factors and soil inorganic carbon content was soil microbial biomass nitrogen > soil water content.The effect of soil microbial biomass nitrogen on soil inorganic carbon content was mainly direct negative effect,water content had direct and indirect effects on soil inorganic carbon content;soil microbial biomass nitrogen and water content jointly lead to changes in soil inorganic carbon content.