Root Exudates Of Dominant Plants And The Effects Of Their Main Components On Soil Microorganisms In Stipa Breviflora Desert Steppe

Root exudates are key factors that maintain the vitality of microenvironment rhizosphere and consititute the different plant rhizosphere characteristics.Plant root exudates play an important role in regulating rhizosphere microbial communities,improving rhizosphere microenvironment and the interaction among species in plant communities.The study of plant root exudates in desert grassland communities helps to explore the physiological mechanism of desert grassland plants adapting to their living environment from the point of view of physiological ecology.Reveal that plants can adjust and control rhizosphere microorganisms through their root exudates,and microorganisms are involved in the transformation of matter in the soil,which will improve the effective nutrients of plants.Thus,the plant growth status can be adjusted to adapt to the living environment.In this study,we digged the roots of Stipa breviflora,Artemisia frigida and Cleistogenes songorica,which are the constructive and dominant species of desert steppe.We collected root exudates by sand and water culture,extracted them with ethyl acetate,and identified their components by means of gas chromatography-mass spectrometry.We simulated three common components of three plants root exudates by chemical reagents,added them to the grassland soil,and then cultured them for three weeks.We determined the V3-V4 of 16 S rDNA gene region of the soil bacteria and ITS1-ITS2 of rDNA gene region of the fungi by an Illumina sequencing technique.We used OTU-based analyses to identify the change diversity and community structure of bacteria and fungi in the soil,which we then combined with the changes of the soil properties.The main results are as follows:1.The root exudates of the Stipa breviflora,Artemisia frigida and Cleistogenes songorica were all shown to contain esters,hydrocarbons,phenols and amides.The contents of the esters were the highest in their exudates.Seven basic components were detected in the root exudates of the Stipa breviflora;eight were detected in the root exudates of the Cleistogenes songorica;and six were detected in the root exudates of the Artemisia frigida.There were three common components in the root exudates of the three plants,namely tributyl acetylcitrate,(Z)-13-Docosenamide and o-Xylene.Due to the relatively high content of the three components in the total root exudates,they were also the main root exudate components of the three dominant species in the Stipa breviflora desert steppe.2.Bacterial diversity was significantly decreased in the soil which was treated with tributyl acetylcitrate and o-Xylene.However,bacterial diversity was promoted at low concentrations and inhibited at higher concentrations in the soil which was treated with(Z)-13-Docosenamide.The three types of root exudates all had significant inhibiting effects on the Gp4,Gp6,Gp25,Gp7,Parasegetibacter,Flavitalea,Flavisolibacter and Niastella of the soil bacterial community.In particular,they all had extremely significant inhibitory effects on the Gp4 and Gp6,which are dominant bacteria in the grassland soil.The three types of root exudates also had significant effects on the Bacillus,Thermoleophilum,Gaiella,Streptomyces,Aciditerrimonas,Solirubrobacter and Conexibacter.In addition,the tributyl acetylcitrate had extremely significant promoted effects on the Sphingomonas and Lysobacter.(Z)-13-Docosenamide had extremely significant promoted effects on the Pseudomonas and Gaiella.The o-Xylene had extremely significant promoted effects on the Pseudomonas,Bacillus and Gaiella.Moreover,the Bacillus,Pseudomonas,Sphingomonas,Streptomyces,Arthrobacter and Thermoleophilum were all have been confirmed to be plant growth promoting rhizobacteria.3.The fungal diversity was significantly decreased in all of the soils which were treated by the three types of root exudates.The tributyl acetylcitrate significantly promote the abundance of Fusarium,which is the dominant fungus in the soil.It also had a significant inhibition on the Penicillium,Aspergillus,Geotrichum,Candida,Xeromyces,Pseudogymnoascus,Phaeosphaeria,Ophiocordyceps,Plectosphaerella,Russula,Phanerochaete and Mortierella.(Z)-13-Docosenamide has a concentration effect on the Fusarium and Trichoderma,which is promoting in low concentrations and inhibiting in higher concentrations.It also significantly promoted the abundances of Penicillium and Aspergillus,and had a significantly inhibited effect on the Phaeosphaeria,Ophiocordyceps and Lecanicillium as well.The o-Xylene had a significant promoting effect on the Mortierella,and a significant promoting effect on the Phoma and Selenophoma in higher concentrations,while promoting in low concentrations and inhibiting in higher concentrations on the Fusarium,yet it had a significant inhibitory effect on the Aspergillus and Gibberella.4.The three types of secretion components significantly improved the content of the available phosphorus and organic carbon in the soil,while the o-Xylene also significantly increased the soil available nitrogen.The tributyl acetylcitrate and(Z)-13-Docosenamide both significantly reduced the soil pH,but the o-Xylene significantly increased it.The Gp16,Rubrobacter,Bacillus,Iamia,Pseudomonas and Lactobacillus of the soil bacterial communities have positive correlations with the available phosphorus and available nitrogen.In the soil fungal community,the Hygrocybe,Cryptococcus,Metarhizium,Malassezia,Cordyceps,Phoma,Selenophoma and Conocybe had positive correlations with the available nitrogen,while the Selenophoma,Conocybe,Phoma,Cordyceps,Emericella,Preussia,Leptospora,Pseudogymnoascus,Trichothecium and Mortierella had positive correlations with the available phosphorus.5.The three types of secretions significantly changed the microbial community in the soil,especially in terms of improving the bacterial community composition in soil.In addition,they all significantly improved the content of the soil effective phosphorus.The o-Xylene also significantly increased the effective nitrogen in the soil.These results reveal that plant roots can secrete organic matter,which changes the composition of the plant rhizosphere microbial community,then improves the microenvironment of the rhizosphere,which may be one of the physiological adaptation mechanism of plants.O-Xylene may be the most effective root secretion component for improving the rhizosphere microenvironment of plants,while Bacillus and Pseudomonas are most likely to be the key microorganisms which promote available nutrients in the soil.