| Desertification is a global environmental problem,which has been disturbing the quality of human life and economic development.The invention of straw checkerboard sand-fixing technology has effectively stopped the process of desertification,especially the planting patterns of planting sand-fixing vegetation on the straw checkerboard,which has better promoted the reversal of desertification.In the restoration of sand fixation of straw checkerboard coupled vegetation,it is of great importance to explore the vegetation-soil-microbe interaction mechanism under the straw checkerboard sand fixation in different measures for understanding the restoration process of the sandy land ecosystem and improving ecological management.In this study,the different sand-fixing vegetation planting patterns of the straw checkerboard in the southern margin of Mu Us Sandy Land for 17 years built-in 2002 was selected as the research object,and the sand-fixing patterns of planting in straw checkerboard with Caragana korshinskii,C.korshinskii×Corethrodendron scoparium,C.korshinskii×Calligonum mongolicum,and C.scoparium×C.mongolicum,and straw checkerboard sand-fixing pattern without planting shrubs and moving dune as control.We employed bacterial 16S rRNA absolute quantitative sequencing and fungal ITS relative quantitative sequencing methods,to investigate the composition and diversity of the nonrhizosphere soil and the dominant rhizosphere microbial communities,and to analyze the physical and chemical properties of the non-rhizosphere soil and rhizosphere soil,and the composition characteristics of vegetation communities.Our study was to reveal the relationship between soil,microorganisms,and vegetation in the sand-fixing ecosystem coupled with straw checkerboard by regression analysis,redundancy analysis and structural equation model,and etc.It is to provide a theoretical basis for the restoration of the sandy land ecosystem.The main results are as follows:(1)Compared with the control,the physicochemical properties of the non-rhizosphere soil were effectively improved by the different sand-fixing vegetation planting patterns.The average soil moisture content in topsoil(SM)of the four sand-fixing vegetation planting patterns was 2.5 times than that of moving dunes,and the average of the total nitrogen(TN),available nitrogen(AN),available phosphorus(AP),and soil organic carbon(SOC)were 2.6,2.2,4.3,and 2.4 times than moving dunes,respectively,which effectively improved the herbaceous community structure under the model of sand-fixing vegetation.The model of sand-fixing vegetation containing C.korshinskii promoted the proportion of gramineous plants,and the sand-fixing model of C.korshinskii×C.scoparium significantly improved the soil physicochemical properties and increased the species diversity,dominance index,and evenness index and aboveground biomass of the herbaceous community.Soil moisture(SM)and N:P ratios were the crucial factors promoting herbaceous communities.The two dominant plants included in this sandfixing model were C.korshinskii and C.scoparium,which also showed the highest coverage,height,and aboveground biomass than the other dominant plants.The aboveground biomass of the dominant plants was closely related to the SM and EC content of the rhizosphere soil.The structural equation model(SEM)revealed that the dominant species of sand-fixing vegetation promoted the development and diversity of the herbaceous community,increased the surface soil moisture,improved the soil physicochemical properties,accumulated abundant soil nutrients,and increased the N:P ratio of soil.(2)The Shannon diversity and OTU abundance of bacteria in non-rhizosphere soil were 1.9 and 45 times higher than those of moving dunes under the different sand-fixing vegetation planting patterns,respectively,while the diversity and abundance of fungi were stable.The composition of the bacterial community was optimized and the dominant bacterial phyla in non-rhizosphere and the rhizosphere bacterial communities of the dominant species include Actinobacteria,Proteobacteria,Acidobacteria,Chloroflexi,and Bacteroidetes.Among the sand-fixing vegetation patterns and the rhizosphere of dominant species,the bacterial abundance was the highest in the sand-fixing pattern of C.korshinskii×C.scoparium.Non-rhizosphere soil and Its dominant rhizosphere fungi under the planting patterns of planting sand-fixing vegetation on the straw checkerboard,were mainly Ascomycota,Basidiomycota,Chytridiomycota,and Mortierellomycota.The non-rhizosphere soil and the rhizosphere of the dominant species had a strong bacteria-bacteria and bacteria-fungus network interaction in the sand-fixing vegetation model of C.korshinskii×C.scoparium,and the abundance of Rhizobium,Nitrosospira,Novosphingobium,Amycolatopsis,Shinella,and Asticcacaulis were formed in their rhizosphere.N:P ratio and TN in non-rhizosphere soil were important factors that positively affected soil bacterial diversity,while C:N,C:P ratio,and SOC were important factors that positively affected rhizosphere bacterial diversity.Non-rhizosphere soil AP is an important factor positively affecting soil bacterial abundance,while the rhizosphere soil N:P ratio is an important factor positively affecting the rhizosphere bacterial abundance.Non-rhizosphere soil pH is an important factor negatively affecting the diversity and abundance of soil fungi,while the rhizosphere soil SOC and pH are the positive and negative factors affecting the abundance of rhizosphere fungi,respectively.(3)Based on the functional prediction analysis of FAPROTAX and FUNGuild,the bacterial functional groups of the non-rhizosphere soil and the dominant rhizosphere were mainly those involved in C and N metabolism,and the abundance of bacterial functional groups of soil and the dominant rhizosphere was the highest under the model of sand-fixing vegetation for two legumes containing C.korshinskii×C.scoparium.Soil AP,available potassium(AK),and N:P were key factors that positively affected the abundance of bacterial functional groups in non-rhizosphere soil,while N:P and C:P were key factors that positively affected the abundance of bacterial functional groups in rhizosphere soil,and TP was a key factor that negatively affected the abundance of bacterial functional groups in rhizosphere soil.The main functional groups in the non-rhizosphere soil of fungi were saprophytic and pathological,and the soil N:P was a key factor that positively affected the abundance of fungal functional groups in non-rhizosphere soil.However,the main functional groups of the dominant rhizosphere fungi were animal pathogens and saprophytes.Soil C:N,C:P,and SOC were the key factors that positively affected the abundance of rhizosphere fungi.SEM revealed that the dominant species improved soil physical and chemical properties with abundant aboveground biomass under the planting patterns of planting sandfixing vegetation,and thus increased soil microbial diversity and abundance.These changes were attributed to the growth characteristics of the dominant plants.The dominant rhizosphere Rhizobiales and Actinomycetales significantly promoted the accumulation of biomass in the dominant plants and established the vegetation-soil-microbiomes interaction driving mechanism.In conclusion,the planting patterns of planting sand-fixing vegetation effectively improve the soil physical and chemical properties,significantly improve soil microbial community composition and abundance,promote the network structure and functional groups of soil microbial interactions abundance,maintain the multifunctionality of the sandy ecological system of soil,improve the plant community diversity and productivity.Among them,the planting pattern of planting two leguminous plants into the straw checkerboard(a combination of C.korshinskii and C.scoparium)is the best sand-fixing pattern for the ecological restoration of sandy land in the southern margin of Mu Us Sandy Land. |
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