Effect Of Rhizosphere Bacteria On The Resistance Of Plant To Stress

Rhizosphere bacteria of plants are the important component of soil ecosystems and plant microecosystem,especially plant growth-promoting rhizobacteria(PGPR)are known to people for improving plant health and promoting growth at abiotic stresses.In this thesis,we evaluated the functions of rhizosphere bacteria from typical desert plants in Minqin and Yanchi by traditional physiobiochemic method and molecular method.Pot experiments by inoculating were performed to evaluate the plant growth promotion and drought and salt stress relief potential of the strain,and analysed the effects of bacteria on plant physiological characteristic and resistance to stress.The main results of the researches were as follows:1)Rhizosphere bacteria of desert plants had various functional properties.Majority of tested strains had the ablity of nitrogen fixation,accounted for 83.33%,in which 20% were able to express the nitrogen fixation gene(nifH);strains with the ablity of phosphorus-solubilizing and IAA producing were accounted for 66.67% and 58.33%,respectively.Fuethermore,27.78% and 47.22% of strains had the ability of producing siderophore and ACC deaminase,in which 23.53% were able to express the synthetic ACC deaminase gene(acd S).Rhizosphere bacteria had high salt tolerance and ranged more than 10% NaCl accounted for 15% of the total number of isolates.Multi-functional bacteria were dominated by Streptomyces,Bacillus and Arthrobacter genera,and majority of groups isolated from Caragana microphylla and Nitraria tangutorum Bobr plants.2)Streptomyces sp.DN-14 obviously promoted the growth of Caragana microphylla and Zea mays seedlings and enhanced their resistence to drought.Strains CN-15 and DN-14 treatments showed a increase in plants growth in different drought stress conditions,significant improvement in the shoot height,root length,leaf relative water content(RWC),fresh and dry mass compared to the control were observed.With the inoculation time change,significant decreasing in malondialdehyde(MDA)content of the two treatment plants under light and middle drought stress,while the control increased and then decreased,and presenting significant difference between them;strains were able to increase the antioxidant enzymes(SOD,POD,CAT)activity,chlorophyll and soluble sugar content,but they showed decreasing trend under high drought stress in later time;in addition,with the increase of drought stress and prolonging time,the electrical conductivity of control plants was increasing all time,while decreasing with strain DN-14 treatments,and stabilized the plasma membrane permeability.Furthermore,strain DN-14 affected Caragana microphylla growth under light drought stress and Zea mays under light and middle drought stress.In conclusion,treatment with strains increased the growth of Zea mays more significantly,and strain DN-14 can promote the growth of Caragana microphylla and Zea mays effectively and enhance their resistance to stress.3)Bacillus sp.AN-6 could promote the growth of Zea mays seedlings and improved their resistance to salt stress.Inoculation of maize plants with CN-15,DN-14 and AN-6,strains CN-15 and AN-6 had significant improvement in the shoot height,root length,leaf water content,fresh and dry mass and photosynthetic parameters compared to the control under l50 and 200 mmol/L NaCl salt stress conditions;moreover,the strains significantly lowered leaf osmotic potential under 150 mmol/L NaCl,and thus increased the osmotic adjustment ability;and reduced Na+content and Na+/K+value.In a word,treatment with strains increased the growth of maize more significantly under l50 and 200 mmol/L NaCl salt stress after inoculation 14 days,AN-6 can effectively improve the salt tolerance of maize and most significant.In this paper,the results indicated that rhizosphere bacteria of desert plants have multiple biological functions,and had effect on promoting growth and enhancing plants resistance to drought and salt stress.It provided a basis for revealing the interaction mechanisms between rhizosphere bacteria and plants,and a new way for controlling desertification.