| Shrubbery is the main type of forest vegetation in arid and semi-arid areas of China,which plays an irreplaceable role in preventing wind and fixing sand,conserving soil and water,purifying air and maintaining regional ecological security.The Kubuqi Desert is located in the arid and semi-arid inland area of northwest China,that is a typical ecological fragile area.Over the years,a large area of artificial shrubbery has been built in the Kubuqi Desert area,which plays a positive role in improving the regional ecological environment and maintaining the ecological balance,and also plays an important role in carbon sequestration.This study we select four typical artificial shrubbery(Caragana korshinskii,Hippophae rhamnoides,Salix psammophila and Corethrodendron fruticosum var.mongolicum)in Kubuqi Desert area as the research object,based on the Landsat8OLI remote sensing image data and sample plot survey data,using the method of stepwise regression,established four shrubbery remote sensing estimation model,and the biomass model method was used to construct biomass model of each organ,the above ground and whole plant for the four shrubs,and analysised the various organ biomass distribution characteristics.We estimated the carbon density of layer,herb layer,litter layer and soil layer in four kinds of artificial shrubbery,analysised the carbon library features in different levels,that can provide a basic reference to estimate carbon reservation of four shrubbery ecosystem systematically and accurately,and can provide scientific support for regional ecosystem conservation,restoration and reconstruction,evaluation of ecosystem service function accurately at the same time.The main conclusions are as follows:(1)The biomass of the four shrubbery is different,from large to small is Salix psammophila forest(4.09 t·hm-2)>Caragana korshinskii forest(2.29 t·hm-2)>Hippophae rhamnoides forest(1.61 t·hm-2)>Corethrodendron fruticosum var.mongolicum forest(0.59 t·hm-2).The average biomass of the whole plant is Salix psammophila(7.42 kg per plant)>Caragana korskii(3.97 kg per plant)>Hippophylla rhamnoides(2.31 kg per plant)>Corethrodendron fruticosum var.Mongolicum(0.32 kg per plant)respectively.There were significant differences in the whole plant biomass among the four shrubs(p<0.001).(2)There were significant differences in the biomass of each organ of the same shrub.The stem-mass ratio,branch-mass ratio,leaf-mass ratio and root-mass ratio of the four shrubs ranged from 0.23 to 0.30,from 0.22 to 0.28,from 0.15 to 0.17,and from 0.26 to0.30 respectively,indicating that the stem,branch or root were the main contributors to the biomass of the whole plant,and the proportion of leaf biomass was the least.There was a significant positive correlation between the aboveground biomass and the underground biomass of the four shrubs(p<0.01),and the aboveground biomass accounted for 65%to75%of the total plant biomass.Caragana korshinskii accounted for the largest proportion of aboveground biomass,followed by Salix psammophila and Hippophae rhamnoides,and Corethrodendron fruticosum var.mongolicum was the smallest.The root-shoot ratios of the four shrubs were all less than 1,indicating that they did not distribute more photosynthates to the underground parts.(3)Different shrubbery herb layer and litter layer have different biomass.The biomass of herbaceous layer from large to small was Caragana korskii forest(0.42 t·hm-2)>Hippophylla rhamnosum forest(0.34 t·hm-2)>Corethrodendron fruticosum var.mongolicum forest(0.30 t·hm-2)>Salix psammophila forest(0.25 t·hm-2).The biomass of litter layer from large to small was Hippophae rhamnoides forest(0.36 t·hm-2)>Caragana korshinskii forest(0.24 t·hm-2)>Salix psammophila forest(0.09 t·hm-2)=Corethrodendron fruticosum var.mongolicum forest(0.09 t·hm-2).There were no significant differences in herb layer and litter layer among different stands(p>0.05).(4)The stepwise regression method was used to establish the optimal biomass estimation models for four shrubbery,and all the equations reached a very significant level(p<0.001).The discrimination coefficients(R2)of the biomass estimation models for Caragana korshinskii,Hippophae rhamnoides,Salix psammophila and Corethrodendron fruticosum var.mongolicum were 0.49,0.51,0.47 and 0.41 respectively,and the prediction accuracy was 72.1%,62.5%,76.5%and 72.2%respectively.The results had a certain reference value.(5)The carbon content is different between different shrubbery and different organs,The carbon content of the whole plant of four shrubs was Hippophae rhamnoides(0.4396)>Salix psammophila(0.4352)>Caragana korshinskii(0.4329)>Corethrodendron fruticosum var.mongolicum(0.4131),leaf carbon content was the highest in all organs of different shrubs.The carbon content of litter layer was as follows:Hippophae rhamnoides forest(0.4915)>Salix psammophila forest(0.4738)>Caragana korshinskii forest(0.4586)>Corethrodendron fruticosum var.mongolicum forest(0.4229).The carbon content of herb layer was as follows:Corethrodendron fruticosum var.mongolicum forest(0.4893)>Salix psammophila forest(0.4783)>Hippophae rhamnoides forest(0.4267)>Caragana korshinskii forest(0.4072).The soil carbon content varied with different shrubbery at different depths,the soil carbon content of Caragana korshinskii forest present a tendency to go down,then up,then down.Salix psammophila forest showed a decreasing trend with the increase of soil depth.The soil carbon content of Corethrodendron fruticosum var.mongolicum forest and Hippophae rhamnoides forest showed a tendency with the increase of soil depth increased first,and dropped dramatically in 60-100 cm depth.(6)The hot spots of carbon density are mainly distributed in the northeastern part of the Kubuqi Desert,while the cold spots of carbon density are mainly distributed in the middle part,indicating that the spatial distribution of carbon density is uneven in the Kubuqi Desert.The northeast part is the region with higher carbon density distribution,and the middle part is the region with lower carbon density distribution.(7)Among the four shrubbery,the carbon density of shrub layer was Salix psammophila forest(3.1519 t·hm-2)>Caragana korshinskii forest(1.9011 t·hm-2)>Hippophae rhamnoides forest(0.8890 t·hm-2)>Corethrodendron fruticosum var.mongolicum forest(0.3768 t·hm-2).The order of carbon density in litter layer was Hippophae rhamnoides forest(0.1629 t·hm-2)>Caragana korshinskii forest(0.1167t·hm-2)>Salix psammophila forest(0.0436 t·hm-2)>Corethrodendron fruticosum var.mongolicum forest(0.0375 t·hm-2).The carbon density of herbaceous layer was as follows:Caragana korshinskii forest(0.1729 t·hm-2)>Hippophae rhamnoides forest(0.1459t·hm-2)>Corethrodendron fruticosum var.mongolicum forest(0.1430 t·hm-2)>Salix psammophila forest(0.1189 t·hm-2).(8)Among the totalcarbon density of the four shrubbery,Caragana korshinskii forest was the highest(35.40 t·hm-2),followed by Hippophae rhamnoides forest(16.18 t·hm-2)and Salix psammophila forest(13.64 t·hm-2),and Corethrodendron fruticosum var.mongolicum forest(13.11 t·hm-2)had the lowest carbon density.The proportion of carbon density in Caragana korshinskii forest,Salix psammophila forest and Corethrodendron fruticosum var.mongolicum forest(0.59 t·hm-2)was the soil layer>shrub layer>herb layer>litter layer,and the Hippophae rhamnoides forest was the soil layer>shrub layer>litter>herb layer. |
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