Study On The Growth-promoting Effect Of Indigenous Plant Growth-promoting Bacteria On Local Typical Pastures And Its Mechanism In Northern Tibet

Recently,vegetation deterioration and soil degradation in Northern Tibetan steppe was a seriously problem,which severely affect the biodiversity of grassland ecosystem and human life.How to improve the efficiency of revegetation effectively in degradaed steppe soil has attracted more and more attention.Soil microbes play an important role in maintaining plant health and amelioration of soil quality.Functional microbial inocula such as Plant growth promoting bacteria(PGPB)and arbuscular mycorrhiza fungi(AMF)showed great potential in improving vegetation restoration.The effect of inocula is determined by plant genotypes and bacterial species.Furthermore,abiotic(water,temperature,nutrients,etc.)and biological factors(microorganisms)in the soil also affect the outcome of plant growth promotion.In order to optimize the functional inocula preparation and improve the efficiency of plant revegetation in Tibetan steppe,low temperature and drought resistant PGPB were successfully isolated from Northern Tibetan soil.Different functional inocula were constructed and inoculated to the rhizosphere of local typical grass.The effects of inoculant on plant growth and environmental microbial community were analyzed.The main results are as follows:(1)By using serial dilution plating method,32 strains of low-temperature-tolerant bacteria were successfully isolated from degraded steppe soil in northern Tibetan,which belonged to Brevibacterium,Bacillus,Paenibacillus,Arthrobacter,Exiguobacterium and Pseudarthrobacter,six genera.All the 32 isolates showed plant growth-promoting properties.Bacillus mycoides TS26 showed higher SID and IAA production ability,and Pseudarthrobacter siccitolerans TS33 displayed the highest IAA production ability.Paenibacillus xylanexedens TS19 showed highest drought-tolerant capacity.The isolated strains exerted different effects on the growth of Poa annua.Pseudarthrobacter siccitolerans TS33 and Brevibacterium sp.TS22 showed higher plant growth promoting effect among all the isolates.(2)The results of pot experiment under cold and drought stress showed that,either single inoculation(P.xylanexedens TS19?Brevibacterium sp.TS22?Bacillusmycoides TS26),or combined inoculation(TS19&TS22 and TS19&TS26)can improve the root development under middle drought stress(relative water content,35%).The combined inoculation(TS19&TS22 and TS19&TS26)showed synergistic promotion effect on biomass of Poa annua.Under severe drought stress(relative water content,15%),treatments with inoculation can effectively adjust plant hormones(ROS,SOD,Pro,ABA)and promote root development and above-ground biomass.The inoculation of strain TS19 showed highest resistance to drought stress and significantly promoted plant biomass and root development.Therefore,suitable inoculants should be selected according to drought stress levels.(3)In the pot experiment with natural Tibetan soil,the addition of functional inocula(PGPB and/or AMF)can alleviate the inhibition effect on plant growth from indigenous soil microbial population.The treatments with single AMF inocula addition showed significant positive effect on the growth of Poa annua(aboveground dry weight,root length and number of leaves);The combined inocula(PGPB+AMF)significantly increase the SOD activity,and reduce the MDA and ROS content in Poa annua.(4)The influence of the inocula on the soil microbial community varied according to inoculant composition.Addition of PGPB significantly lowered the?-diversity of soil microbial community.There was a significant difference in the?-diversity of bacteria in the soil supplemented with AMF.The enrichment of Xanthomonas and Pseudomonas,which enbowed plant growth promotion or biocontrol capacities,maybe the reason for its outstanding effect on Poa annua growth.The discoveries in this stuty provide important value for the preparation and applicatoin of effective PGPB inocula.In summary,this study successfully isolated low-temperature tolerant and drought resistant PGPB from the degraded soil in Northern Tibetan Steppe.Under mimicking the local environmental conditions in Tibetan Plateau,the significant positive effect of functional inocula on the plant growth and stress resistance capacity were proved.The influence of inocula on the environmental microbial community and the mechanism of the functional inocula on the plant growth promotion were clarified.It showed the great potential of indigenous PGPB in the plant restoration of degraded steppe in Northern Tibetan Plateau.This study provides valuable inocula resources,also support the plant revegetation in Tibetan Steppe with important theoratical and pratical guidance.