| With the development of social economy,human activities have significantly changed the global environment,and unreasonable exploitation have caused great damage to the original natural ecological system.Coupled with the emergence of a series of problems such as environmental pollution and energy depletion,the balance of the earth's ecosystem has been seriously jeopardized,and the global economy has also suffered tremendous damage.The Tibetan Plateau is a unique geographical unit with a unique natural environment and social and economic development conditions that are very different from those in other regions.The fragile ecological environment and the desertification area are seriously affecting the industrial and agricultural production of the Tibetan area and the living standards of the Tibetan people.The comprehensive development and economic development of the autonomous region pose a direct threat.As one of the main constructive species on the plateau,the sophora psammophila has the ecological functions of sand fixation,soil and water conservation,and considerable value for feeding and medicinal purposes.Due to the special geographical environment of the distribution of sophora psammophila,it suffers from low temperature and strong wind for a long time in a year,and it is also affected by many unfavorable factors such as grazing,man-made felling,floods and drought.Coupled with the low afforestation survival rate of sophora psammophila,it has been restricting the ecological restoration and development of the Yarlung Zangbo River Basin.Rhizosphere growth promoting bacteria(PGPR)produced in the process of plants growth,including growth regulators(plant hormones),nitrogen-fixing bacteria,phosphate-dissolving bacteria,the growth hormone and so on,is a new type of microbial fertilizer that can improve crop yield,relieve stress and protect environment.It directly affects the metabolism of plants on the one hand and improves the adaptability of plants to absorb other nutrients from the soil on the other hand,which directly or indirectly make it more easily for plants to absorb nutrients and prevent nutrients loss.It is of great important to select a new type of microbial fertilizer with high-efficient growth-promoting.Growth promoting bacteria with high efficiency.In order to obtain efficient rhizosphere growth promoting bacteria of sophora psammophila with nitrogen fixation,phosphorus dissolving and indole acetic acid(IAA),the experiment was carried out at the Biotechnology Center of agriculture and Animal Husbandry College to explore the phosphorus dissolving,nitrogen fixing and IAA producing abilities of the obtained rhizosphere growth promoting bacteria,and the antagonism of the strains was determined by plate confrontation method,and the physiological and biochemical characteristics of the strains were studied by Gram staining.To study the effects of screened strains on seed germination and seedling growth of sophora psammophila under drought stress,and to establish a pot experiment under simulated natural drought condition to test the growth-promoting ability of the strains,and to explore the effects of PGPR inoculation on seedling growth of sophora psammophila under drought stress.The final results are as follows:(1)In this study,12 strains of nitrogen-fixing bacteria,10 strains of organic phosphorus,4 strains of inorganic phosphorus,and 10 strains of IAA were obtained from the rhizosphere soil of sophora psammophila at flowering and podding stages collected from Miling County,Lang County,Jiacha County,Linzhou County,Bailang County,Lhasa City,Rikaze City,Gongga County and zhanang County.(2)The semi-micro Kjeldahl method and the molybdenum-antimony colorimetric method were used to determine the nitrogen content and available phosphorus content of the strain.The highest nitrogen content was 225?g/m L,followed by strain N23-3,with a nitrogen content of 200?g/m L.Among the 14 strains of phosphorolytic bacteria,the maximum D/d ratio of strain SR21-1 is 3.8,and the minimum D/d ratio of strains SR15-1 and SR10-6 is 2.0;the strain with the highest effective phosphorus content in phosphate-solving bacteria is SR19-2 The effective phosphorus content is 96.13?g/m L,followed by SR19-1 at 92.13?g/m L.The strain with the lowest available phosphorus content is SR10-3,the available phosphorus content is only 33.25?g/m L,the size of the dissolved phosphorus circle is also small,and the D/d ratio is 2.4.Among the sceened strains,10 strains had the ability to secrete IAA,the highest yield of IAA was from SR26-3,43.28mg/L,the lowest yield of IAA was from SR21-1,19.02 mg/L.(3)The results of antagonistic experiment showed that the screened strains N40-4 and N22-5 both had antagonistic effects on wheat sheath blight,wheat scab,wheat root rot,potato dry rot and corn blotch,of which N21-1 had no antagonistic effect on potato dry rot,SR19-2 had no antagonistic effect on wheat scab and had good inhibitory effect on the other four pathogens.Most of the strains had good inhibitory effect on wheat scab.Wheat root rot and corn blotch.In comparison,the inhibition of the strain on wheat blight and potato dry rot was relatively weak.(4)The results of PGPR on seed germination and growth promotion under PEG simulated drought stress showed that during seed germination,inoculation with bacterial suspension had a great effect on seed germination of sophora psammophila.When inoculated with nitrogen-fixing bacteria and phosphate-dissolving bacteria during seed germination,except for N35-2 and SR22-3,the other strains had a definite effect on seed germination,among which the strains N21-1 and SR21-1 had the best effect on seed growth promotion.Under the influence of different PEG concentration,the seed germination of CK1(aseptic water condition)and CK2(organic phosphorus control medium)and various indexes were comprehensively analyzed,and different strains treated with different PEG concentration gradient showed different promotion or inhibition on seed germination,among which the overall evaluation of SR21-1 and SR26-3 were the best,drought tolerance grade was first-class.Under simulated drought conditions,seed germination and drought resistance of locust were significantly promoted.(5)Observation of the morphological characteristics of the strains revealed that the two groups of strains were white,opaque,and raised.Among them,SR21-1 is elliptical,toothed edge,the surface is relatively dry;SR26-3 is round,the edge is complete,the surface is relatively moist.Observation of the cell characteristics of the strains revealed that the morphology of SR21-1 and SR26-3 cells were rod-shaped,and none of them produced spores,and the Gram stain was negative(G~-);Preliminary results of 16S r DNA molecular identification of the strain showed that the identification result of strain SR21-1 was Bacillus mangolovi;the identification result of strain SR26-3 was Serratia Plymouth.(6)Under natural drought stress,the pot experiment of inoculating PGPR on the seedling of sophora psammophila under drought stress showed that the contents of proline and malondialdehyde in the seedling of sophora psammophila under drought stress changed with different drought time,and the content of chlorophyll increased obviously compared with CK after inoculating with PGPR.This indicated that inoculation of growth-promoting bacteria could promote the synthesis of chlorophyll,significantly improve the photosynthetic rate,and promote the growth of sophora psammophila.The test results show that SR26-3 and SR21-1 obtained in the final screening have good drought tolerance,and can be used as an excellent strain to alleviate the growth of sand locust under drought stress.It provides a scientific and rational theoretical basis for the screening of rhizosphere growth-promoting bacteria in the later period. |
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