Study On The Distribution Characteristics And Influencing Factors Of Root And Soil Carbon In The Woodland On The Loess Plateau

The project of returning farmland to forest and grassland in the Loess Plateau is of great significance to the carbon sink and carbon cycle of terrestrial ecosystem.The carbon pool of forest ecosystem is generally composed of aboveground part of vegetation,underground root system,soil and litter.Roots connect the soil with the atmosphere and affect the carbon cycle of ecosystem with plants.Meanwhile,roots are also an important source of deep soil organic carbon pool.Due to the difficulty of deep soil sampling,the content and distribution characteristics of soil organic carbon and inorganic carbon in vertical profile are not very clear,and the root measurement is difficult,time-consuming and not necessarily accurate.At present,most of the researches are focused on the aboveground part of vegetation and shallow soil,while the researches on the underground part of vegetation and deep soil are relatively less.In this study,the forest ecosystem in the Loess Plateau was taken as the research object,and 527 underground biomass and background data were collected through the project of ecocarbon,and the distribution and influencing factors of the underground biomass of the forest ecosystem were analyzed.In addition,based on five experimental stations of Shenmu,Suide,Ansai,Changwu and Fuxian in the Loess Plateau,the soil samples and root samples of 10 m deep soil profile were analyzed by field deep sampling,indoor test processing and data analysis.The distribution characteristics of soil organic carbon and inorganic carbon in artificial forest land in loess hilly region were elucidated.The differences of soil carbon under different rainfall,tree species,shady slope and sunny slope site conditions were analyzed.The influencing factors of soil organic carbon and soil inorganic carbon were discussed.The relationship between deep soil carbon,soil moisture and fine root biomass was revealed.The effects of root organic matter and soil moisture on soil carbon storage were explored.The results are as follows:(1)The underground biomass in forest ecosystem in the Loess Plateau ranged from11.99 Mg/hm~2 to 27.46 Mg/hm~2.Abiotic factors had dominant influence in the underground biomass,particularly for the rainfall and topography.The order for underground biomass was brown>cinnamon>lithologic soil in different soil types,coniferous>coniferous broad-leaved mixed>deciduous broad-leaved forest in different forest types,hillly and mountainous>plateau and plain terrain in different topography respectively.The distribution of underground biomass on the slope was:the foot of mountain slopes>upper,middle and lower slope>flat land.There was no significant difference between human activities and animal activities.We found that the proportion of biotic and abiotic factors on the underground biomass was severely affected by longitude and latitude.It was 68.9%and 31.1%with longitude and latitude factors,otherwise it was 81.1%and 18.9%,respectively.The results indicated that latitude and longitude had a strong correlation with other factors.(2)Surface soil organic carbon contributed the most to soil organic carbon pool,deep soil contained rich inorganic carbon pool,and inorganic carbon contributed the most to deep soil inorganic carbon pool.The content of soil organic carbon in Loess soil was significantly higher than that in aeolian sandy soil(p<0.05).In different soil layers,soil organic carbon content showed the following order:topsoil(0—40 cm)>subsoil(40—200 cm)>deep soil(200—1000 cm),which was opposite to the distribution characteristics of soil inorganic carbon content.With the increase of rainfall(rainfall:Shenmu<Suide<Ansai<Changwu<Fuxian),the coefficient of variation of soil organic carbon content in profile increased,and the contents of soil organic carbon and inorganic carbon in horizontal and vertical distribution showed:Fuxian,Changwu>Ansai,Suide>Shenmu.The content of soil organic carbon in Fuxian was significantly higher than that in Suide and Shenmu.The content of soil organic carbon in sunny slope was lower than that in shady slope.the content of soil organic carbon reached the maximum in surface soil and gradually decreased with the deepening of soil layer.The soil inorganic carbon content of Robinia pseudoacacia forest was lower than that of Pinus tabulaeformis forest.Soil organic carbon can be transformed into inorganic carbon,and its distribution is greatly affected by rainfall.In the final analysis,soil water content and fine root biomass affect soil organic carbon and inorganic carbon.(3)The content of soil organic carbon(SOC)in deep layer is not only affected by vegetation root system,but also limited by soil water content(SWC).The distribution trend of soil organic carbon content,inorganic carbon content and total soil carbon content is:from top to bottom ladder decline.Most of the soil organic carbon existed above 40 cm soil and decreased with depth.The SOC content below 40 cm was between2.17—2.55 g/kg.The content of soil inorganic carbon increased gradually from the surface layer to the deep layer,but always between 0.67—0.94 g/kg.There was a linear relationship between soil moisture and root biomass(UBM)and soil organic carbon content in Robinia pseudoacacia forest and Pinus tabulaeformis forest.When SOC<15 g/kg,it was in accordance with the quantitative relationship,SOC=0.697 UBM+0.459 SWC.The content of soil inorganic carbon is affected by many factors,but there is no obvious rule in vertical profile.Soil carbon content is affected by underground biomass.The study of underground biomass can not only reflect the growth status of vegetation,but also provide a theoretical basis for the study of underground carbon pool.This study has a certain significance for the related research of underground biomass estimation,which can be used as the basis for estimating organic carbon,and even provide some basis for remote sensing.It can also provide a reference for explaining how trees adapt to the environment through the root system,and putting forward suggestions for forest management.The distribution characteristics of soil carbon can provide a reference for estimating soil organic carbon pool and inorganic carbon pool.The influencing factors and prediction models of soil carbon can provide a theoretical basis for the study of deep soil carbon storage.