Diversity Of Bacterial Soil Community And Its Influencing Factors In Rhizocompartments Of Three Leguminous Plants In The Mu Us Desert,China

Leguminosae has always been an important component of various ecosystems in the world due to its high species diversity and wide tolerance in various global ecosystems.Hedysarum mongolicum,Hedysarum scoparium and Caragana microphylla are widely distributed in desert and sandy land of China These three legumes play an important role in fixing soil,improving soil fertility,preventing wind and fixing sand,and vegetation restoration by virtue of their excellent characteristics,such as strong root sprouting ability,deep taproot and symbiotic nitrogen fixation with nitrogen fixing bacteria in soil.The soil microorganisms actively participate in the transformation of important substances and energy in the process of plant-soil interaction,affecting and regulating plant growth.However,most of the current researches usually only focus on one or a relatively small process of plant physiology and biochemistry in the nutrient cycle,ignoring the changes in soil microbial community diversity and structural composition and their influence.In response to these problems,this study evaluated the effects of different rhizocompartment types(i.e.,root,rhizosphere soil,root zone soil,and inter-shrub bulk soil)on the composition and structure of soil bacterial communities,and explored the soil under the desert legume shrubs The status quo of the diversity of microbial communities,and the influence and changes of soil physical and chemical factors in the interaction of plant-soil-microbes.We applied 16 S r RNA highthroughput gene sequencing technology and conventional soil physical and chemical indices measurement methods to determine the diversity,structural composition,and relationship between bacterial communities and environmental factors in the roots of three xerophyte legumes in the Mu Us Desert.Characterized and explored the process of screening and enriching endophytic bacteria in the roots of three xerophyte legumes;finally determined the core bacterial group closely related to the growth and development of these three legumes.The main conclusions are as follows:(1)The content of nutrient elements in the root of desert xerophyte legumes showed a trend of significant enrichment of nutrient elements to the rhizosphere in the soil under and between shrubs(P <0.05).We found that the diversity of endophytic bacterial communities in roots is much lower than the diversity of soil bacterial microbial communities under shrubs.There are significant differences between the root samples of three desert legumes and the soil samples under shrubs in alpha diversity.Diversity indices of soil samples was significantly higher than the plant root samples,and all reached the maximum in the rhizosphere soil(P < 0.05).Plant species and rhizocompartment type jointly affect the alpha diversity of soil bacterial communities under and inter-shrub bulk soil,but rhizocompartment type plays a leading role.The pH and the nitrogen nutrient were the main driving factors for the alpha diversity of bacterial communities in the root zone of three xerophytic legumes.(2)At the phylum level,the endophytic community of xerophytic legumes was mainly composed of Proteobacteria,Actinobacteria,and Bacteroidetes.The relative abundance of these dominant phyla accounted for more than 96-99% of the total bacterial community in each rhizocompartment.Xerophytic legumes have a significant hierarchical enrichment effect on specific bacterial groups through the rhizocompartments.(3)Through rhizocompartments,xerophytic Leguminosae plants can screen and enrich specific dominant bacterial groups in the soil step by step from the inter-shrub bulk soil to the root system,while other dominant bacterial groups show a significant decreasing trend from the inter-shrub bulk soil to the root system step by step(P < 0.05).The co-network of bacterial communities among rhizocompartments shows that specific dominant bacterial groups in rhizocompartments have complex biological interactions with host plants or other bacterial species,which directly or indirectly control the assembly process of the structural composition of the entire bacterial community.The components of the three xerophytic legume core bacterial groups were mainly induced and enriched by host plants.(4)The genotype of plant species can determine the structure and composition of microbial communities in root tissues and underground soil to a certain extent.The bacterial communities in root system and rhizosphere soil are mainly affected by nutrient elements and soil water,while the bacterial communities in the root zone soil and the inter-shrub bulk soil are mainly affected by ammonium nitrogen and pH.Some members of the core bacterial group that are enriched by the screening and enrichment of plant roots in the root region are mainly affected by soil water and nutrient elements,while other members of the core bacterial group that are reduced in the root system relative to the other three root systems are mainly affected by ammonium nitrogen And pH.This study revealed the diversity and structural composition of soil bacterial communities in the rhizocompartments of three xerophyte legumes,and found that xerophyte legumes have a hierarchical screening and enrichment mechanism for beneficial bacteria and microorganisms in the soil through the four rhizocompartments.The relationship between the bacterial community and environmental factors in the root zone of desert legumes was explored.This provides a theoretical basis for the restoration of desert ecological vegetation based on the study of the interactions between desert xerophytes and soil microorganisms,and provides data to support the identification of plant-related dominant bacteria and the preparation of soil improvement inocula in the future.