Response Mechanism Of Sandy Soil Microorganisms To Different Ecological Restoration Measures

Climate change and over-cultivation have caused desertification,and vegetation restoration is key to halting further land degradation and rebuilding degraded ecosystems.Since the implementation of the "Three-North Shelter Forestation Project",a total of 30.149 million hectares of afforestation area has been completed,and the forest coverage rate of the project area has increased from 5.05% to 13.59%.Especially,the vegetation coverage rate of the Mu Us Sandy Land has reached 28.9%,ensuring regional ecological security.The sustainable management and healthy development of plantation communities are important issues for the of ecological environment construction in northwest China,which is limited by the arid climatic environment and poor soil nutrient conditions in wind-blown sandy areas.At present,how to further stabilize and improve the ecological service function of plantation communities in the project area has become a hot issue concerned by relevant management departments and academia.In this study,the natural and artificial vegetation restoration areas of Mu Us Sandy Land were selected to explore the relationships between environmental parameters and soil microbial diversity,community structure and microbial interaction profiles by field experiments and high-throughput sequencing technology,to reveal the spatial variability of microorganisms involved in the carbon and nitrogen cycles under the natural vegetation restoration patterns,to discover the relationship between artificial vegetation restoration patterns and comprehensive soil fertility,to elucidate the microbial mechanism of soil fertility improvement under different ecological restoration measures,and to propose appropriate vegetation allocation patterns and regulatory approaches for providing the scientific basis of sandy vegetation restoration and reconstruction.The main results are showed as follows:First,the abundance of nitrogen fixation gene(nif H)was significantly decreased,while the abundance of nitrification(amo A-AOA + amo A-AOB)and denitrification(nir K + nir S +qnor B + nos Z)genes showed significant increase or fluctuation increase trends,during the restoration of natural vegetation in desertified soil.During the restoration of natural vegetation,the sum of nitrogen fixation and nitrogen mineralization genes abundance were significantly decreased,the abundance was no significant difference in soil profile in the early stages of vegetation restoration.The abundances of nitrification genes were increased significantly,the abundance was no significant difference in soil profile in the early stages of vegetation restoration.The abundances of denitrification genes were significantly increased,there were significant differences in soil profiles in the late stages of vegetation restoration.The abundances of available nitrogen storage potential genes(nif H + chi A + AOA + AOB)/(nir K + nir S + qnor B + nos Z)showed a increasing trend first,and then decreasing.Moreover,vegetation cover was positively correlated with other nitrogen cycle genes except nitrogen fixing genes,indicating that natural vegetation restoration enhanced the intensity of nitrogen cycling.Second,during natural vegetation restoration,the diversity and richness of autotrophic microorganisms significantly increased and the microbial community structure was significantly differentiated.The assembly process of autotrophic microbial community changed from stochastic process to deterministic process.RubisCO activity was highest in the early stage of vegetation restoration,indicating that carbon-sequestering microorganisms were more active in nutrient-poor soils.There were significant differences in bradyrhizobium abundances during vegetation restoration,illustrating the important role of bradyrhizobium in carbon fixation.The relative abundances of core autotrophic microorganisms were significantly positively correlated with RubisCO activity,and core autotrophic microorganisms with the same ecological habits were the most important drivers of RubisCO activity.Third,the soil organic carbon content and microbial biomass nitrogen were significantly higher in leguminous and mixed forests than in non-leguminous and control,while total nitrogen and available phosphorus contents,p H and electrical conductivity were significantly lower;total phosphorus was significantly higher in mixed forests and controls than in leguminous and non-leguminous.The three patterns of artificial vegetation restoration improved soil microbial diversity,interaction complexity and stability,response microbial numbers and classification,nitrogen cycling intensity and photosynthetic intensity,as well as influenced microbial community structure.Moreover,the positive effects of leguminous forest and mixed forests on microorganisms were better than non-leguminous forest.The abundance of bacillus was significantly increased with the restoration of artificial vegetation,which in mixed forests > leguminous > non-leguminous > control.The abundance of bacillus was significantly correlated with soil quality,microbial diversity,nitrogen fixation gene abundances and photosynthesis intensity,indicating that bacillus played important roles in the restoration of artificial vegetation in desertification ecosystem.Fourth,under artificial vegetation restoration patterns,the bacterial community was dominated by deterministic community assembly process,while the arbuscular mycorrhizal fungal community was dominated by stochastic community assembly process.Among different vegetation restoration patterns,bacterial communities were more similar,and arbuscular mycorrhizal fungal communities were more different.There were strong linear relationships between bacterial phylogeny and environmental parameters,while arbuscular mycorrhizal fungi showed weak correlations.Environmental factors explained more bacterial community structure variation(12%)than that of arbuscular mycorrhizal fungi(6%),which mainly because arbuscular mycorrhizal fungi have higher nutrient uptake efficiency and stronger resistance to environmental changes than bacterial community.In addition,bacterial interactons were more complex than that of arbuscular mycorrhizal fungi.Finally,the co-cultivation experiment of biomass(straw)and functional flora(bacillus)for sandy plantations showed that the straw + bacillus treatment significantly improved soil fertility;bacillus treatment increased microbial diversity,network complexity and stability;straw treatment reduced the diversity of microbial diversity,network complexity and stability,but not the comprehensive soil fertility level,which mainly because straw addition increased soil nutrients and nutrient-rich microorganisms but reduced the abundance and classification number of oligotrophic microorganisms that were originally dominant.Multivariate ANOVA showed that bacterial diversity and community composition were only affected by regulatory measures,while fungi were affected by both regulatory measures and vegetation restoration patterns.The structural equation model analysis showed that the treatment of straw,bacillus and straw + bacillus indirectly affected comprehensive soil fertility by affecting soil bacterial and fungal diversity,community composition and interaction complexity,in which fungal community composition had the greatest influence on comprehensive soil fertility,indicating that in poor habitats fertilization could stimulate the regulatory effect of fungal communities on soil ecosystem functions.