Effects of Plant Growth-promoting Rhizobacteria on Physiological Characteristics and Phosphorus Uptake and Utilization of Apple Seedlings under Arid Environment
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【Author in Chinese】 张超；
【Author's Information】 西北农林科技大学， 环境工程， 2017， 硕士
【Abstract】 It is a hotspot to study the adaptability of plants in arid environment by transforming foreign genes or inoculating synthetic bacteria in recent years.Plant growth-promoting rhizobacteria（PGPR）refers to beneficial bacteria that survive in the plant root circle and have a promoting effect on plant growth or antagonism to pathogens.The research on PGPR at home and abroad mainly focused on promoting plant growth,activating soil nutrients,reducing chemical fertilizer application and improving plant inducing system resistance,but there are few studies on apple resistance.In present study,we isolated a rhizosphere-promoting bacteria named YX2（Psdeuomnoda fluoerncne）from the rhizosphere of dryland orchards in the Loess Plateau,which had both ACC-deaminase activity and phosphate dissolved ability.By using pot experiments,we inoculated YX2 to ‘octagonal Begonia’ apple seedling rhizosphere,and four different drought stress gradients（normal water,light drought,moderate drought and severe drought）were set up by controlling soil moisture to study the effects of inoculating YX2 on drought resistance of apple seedlings and activating absorption of phosphorus in soil.The main results are as follows:（1）With the increase of drought stress,the relative water content and chlorophyll content of leaves of seedlings decreased gradually,the leaf relative conductivity increased gradually.Inoculating YX2 could increase the relative water content and chlorophyll content of leaves and significantly decrease leaf relative conductivity in arid environment.Drought stress reduced the photosynthetic rate（Pn）and stomatal conductance（Tr）of apple seedlings.Inoculation of YX2 could increase Tr and alleviate the inhibition of drought stress on Pn,and alleviating effect was significant under moderate drought,whose values of Pn and Tr enhanced by 6.80% and 15.00%,respectively,compared with the non-inoculation treatment.Inoculation of YX2 could inhibit the decrease of maximum photochemical efficiency,actual photochemical efficiency and photochemical quenching coefficient of seedlings under drought stress,and inhibit the increase of initial fluorescence and non-photochemical quenching coefficient,and the best overall effects were under moderate drought.（2）Under normal water treatment,the effects of inoculating YX2 on antioxidant enzymes（catalase,peroxidase,superoxide dismutase）,osmotic adjustment substances（proline,soluble sugar,soluble protein）and membrane lipid of leaves were less.With the increase of drought stress,the inoculation of YX2 could increase the activity of antioxidant enzymes and reduce the accumulation of osmotic regulators and malondialdehyde at different extent,and the effect of YX2 was the most significant in moderate drought.（3）The drought resistance of seedlings under different drought stress was evaluated by principal component analysis and membership function method.The results of principal component analysis showed that the highest score of the main component 1 and the main component 2 were malondialdehyde and transpiration rate respectively under the non-inoculation treatment.Under the YX2 treatment,the highest score of the main component 1 and the main component 2 were malondialdehyde and transpiration rate,respectively,which indicated that inoculation of YX2 treatment had little effect on the contribution rate of main component.The results of subordinate function analysis showed that the YX2 treatment affected the drought resistance of seedlings.The average membership value of the seedlings under the YX2 treatment was higher than no inoculation treatment no matter what kind of moisture state,and the increase was significant in the light and moderate drought,increased by 9.19% and 10.12% compared with non-inoculation treatment,respectively,so that seedlings had stronger drought resistance.（4）No matter what water conditions,inoculation of YX2 treatment increased the dry matter biomass and total phosphorus content of seedlings,enhanced apple root acid phosphatase activity,soil available phosphorus content and soil alkaline phosphatase activity,and decreased soil total phosphorus content.The contribution rate of YX2 absorbing phosphorus of under different water conditions was ranking that moderate drought> normal water> light drought> severe drought.The contribution rate of YX2 absorbing phosphorus was positively correlated with root acid phosphatase,soil available phosphorus and soil alkaline phosphatase.（5）Inoculation of YX2 promoted the growth of seedling roots and increased the root vigor,the total root length and root activity were significantly increased under light drought.In this study,the contents of five organic acids（oxalic acid,malic acid,tartaric acid,succinic acid and citric acid）in root exudates were determined.Inoculating YX2 increased the content of organic acids in roots,and increasing by 0.012 0.035 mg·L-1·2h-1.Oxalic acid is main secretion,whose amount accounted for about 50% of the total secretions.Meantime,inoculation of YX2 also increased the contents of amino acids and soluble total sugar in the secretions.The enhancement of these secretions could improve the soil rhizosphere ecological environment.In this study,we investigated the effecting mechanism of rhizosphere-promoting bacteria YX2 with phosphate dissolved ability on the drought-resistant physiology of apple seedlings and the absorption and utilization of phosphorus in soil under drought stress.The results showed that the overall effect of YX2 inoculation was better in light or moderate arid environment,which provided new ideas and techniques for improving the drought resistance and nutrient utilization of plants by using PGPR interacting with plants in arid or semi-arid areas.