| Tibet, one of the five major traditional pastoral areas of China, is named by "the roofof the world". However, Ali region is the roof of the roof of the world with vast grassland,used as the main substance basis of grassland animal husbandry development Ali region.Mainly plateau frigid desert grassland and ecological environment is fragile, is highlysensitive to the response of the global change and human activities, ecosystem and theenvironment relations to its criticality and the unique biological adaptation mechanism asthe basic characteristics, there are unique, rare biological resources. There has become afocus of many scholars because of its special geographical features and abundant naturalresources. Research on special geographical microbial resources laid the foundation forresources protection and resources application.In present paper, the physicochemical properties of plant rhizosphere soil from fourdominant forages (Elymus dahuricus, Avena sterilis, Medicago sativa and Poa pretensis) inAli region, Tibet, was measured using routine analysis method. The number anddistribution of bacteria and PGPR (plant growth promoting rhizobacteria) was determinedand analyze the correlation between the nutrient content of rhizosphere and number anddistribution of bacteria. The PGPR strains were selected and identified based on themeasurement of nitrogen fixation capacity, phosphate-solubilization capacity and IAAsecretion capacity. The potential PGPR were used for in vitro inoculation experiment andpot inoculation experiment, respectively in order to study the effects of PGPR on thegrowth parameters of Elymus and colonization activity in the rhizosphere of Elymus, andexplore the phosphorus-solubilizing mechanisms of several strains. The results wereobtained as follows：1. Different plant rhizosphere soil physical and chemical properties, the number ofbacteria and PGPR strains and significant distribution differencesThe nutrient content of four plant rhizosphere soils was low, the supply ability of totaleffective soil nutrient was weak, and significant difference was detected for nutrientcontent and the number of distribution in the rhizosphere of different plants, there was acorrelation between soil physical and chemical property of rhizosphere, nutrient contentand the number of bacteria. There were222strains of PGPR were isolated from therhizosphere of four tested plants, consist of71strains nitrogen fixing bacteria,73strains soluble inorganic phosphorus strains and78strains dissolving organic phosphorus strains.The number of bacteria was presented as RS (root soil)> NRS (soil away from roots)> RP(rhizoplan or surface of roots)≧HP (histoplan or interior of roots), having an obviousrhizosphere effect.2. PGPR strain grows characteristic difference was differentThe nitrogen fixation ability of71azotobacter strains were determined by using theacetylene reduction assay method (ARA) while the phosphorus-solubilizing activity andIAA secretion capacity of222strains were measured and screened base onphosphate-solubilizing ring method, molybdenum blue method, Salkowski colorimetrymethod. The results indicated that28strains had good nitrogenase activity, which variedfrom1.08to446.63nmol C2H4·h-1mL-1;15strains have good ability of dissolvinginorganic phosphorus, the values of D/d were between1.12and1.69and the amount ofdissolved phosphorus in1.66-40.89μg/mL while32strains can dissolve organicphosphorus, the values of D/d were between1.23and3.47and the amount of dissolvedphosphorus in11.05-26.03μg/mL;38strains have the ability to secreting IAA, itssecretion was in7.63-26.20μg/mL.3. Good PGPR strain mainly were the bacteria belong to the pseudomonas andbacillus genusThe potential PGPR were identified based on16s rDNA, the results showed that eightstrains (PWXZ10, PYXP1, NXZ8, NXZ17,003PWXZ3,003NXZ4,003NXZ6,003NXZ9),having high homology with Pseudomonas sp., were identified as Pseudomonas genus;Strain PYXZ1, PWXZ6, NXZ4have high homology with Pseudomonas fluorescens,therefore identified them as Pseudomonas fluoresceut while Strain PWXZ23, NXP17wereidentified as bacillus genus for having a very high homology with Bacterium.4. Good PGPR strains in plant rhizosphere colonization, the success of plant growseffect were remarkableInoculants, composed of17stains soluble phosphorus bacteria and9strainsazotobacter were used for inoculation experiment. The results indicated that the height,aboveground biomass and underground biomass of Elymus dahuricus treated by PGPRinoculants were significantly higher than that of control (CK), different inoculants hadsignificant effect on the root parameters of Elymus dahuricus (P<0.05). Strains003PWXZ6, NXP17had the most obvious promoting effect on plant height while PYXP1 and NXP17had positive effect on aboveground biomass, underground biomass and totalweight. The root shoot ratio of PWXZ10and003NXZ5were the highest while StrainPYXZ7and NXZ9had the maximum root volume. Root length, root surface area, rootvolume of plant treated by PYXZ19were maximum. The effects of different stains on totalroot length, root surface area, root volume and their distribution were different, there is thehighest ratio among plant root length, root surface area, root volume between strainPYXZ19treatment root diameter greater than0.45mm and strain NXZ16treatment rootdiameter greater than0.15mm. Strains can be successful colonization on the rhizosphereof Elymus dahuricus, and had a significant impact on the phosphorus, nitrogen content ofaboveground, underground part and the whole plant and protein content of abovegroundpart (P<0.05), the phosphorus content of aboveground, underground part and the wholeplant after inoculating003PWXZ6was the highest while NXP17had the highest nitrogencontent of aboveground, underground part and the whole plant and protein of abovegroundpart. Therefore, the comprehensive analysis of all parameters confirmed that these strains(003PWXZ6、NXP17、PYXP1、PWXZ10、003NXZ5、PYXZ7、NXZ9) had the potentialto produce biofertilizer.5. Mechanism of dissolving phosphorus strains were diverseSix solubilizing phosphorus bacteria were cultivated in liquid LB medium, theavailable phosphorus content, change of pH and sucrase activity, phosphatase activity, thetype and content of organic acid of culture solution were detected in different time (2,4,6,8,10d) by using molybdenum antimony colorimetric method, pH meter method,3,5-dinitrosalicylic acid method, pyrocatechol phosphate disodium colorimetric methodand high performance liquid chromatography (HPLC) method, respectively, and analyzedthe correlation of available phosphorus content and other index. The results indicated thatthere had a linear correlation (P<0.01) between available phosphorus content and pH valuefor the10d PKO and Mengjinna liquid medium. All treatments training within10d, thesucrase activity of PKO were superior to that of Mengjinna, strain PWXZ6in PKO brothand strain PYXZ23in Mengjinna broth had certain positive correlation between availablephosphorus content and sucrase activity(P<0.05). Meanwhile, there had a significantlypositive correlation relationship between available phosphorus content and phosphataseactivity of broth. All the strainscultured in broth can secrete a certain amount of lactic acid,formic acid, acetic acid, citric acid, tartaric acid, oxalic acid, malic acid, fumaric acid, succinic acid, etc., however, the type and amount of organic acid depended on strain.During cultivation period, the dynamic change of total organic acid secreted by strains wasbimodal curve.6. Soluble phosphorus strains of dissolving phosphorus approaches were diverseIn this study, strains PYXZ1when dissolved inorganic phosphorus is the main way toreduce the pH of solution and the role of phosphatase, strain PWXZ10the main way ofdissolving phosphorus was to reduce the pH of solution, strain PWXZ6the main way is toreduce the pH of solution, the common role of sucrase, phosphatase, and organic acids,strain PYXZ3solution was the main way of the combination of sucrase, phosphatase, andorganic acids. |
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