Isolation And Identification Of Potassium Solubilizing Bacteria And Their Growth Promoting Effects On Tobacco

Potassium is a major plant essential nutrient,which plays a key role in plant physiological development and metabolism,and effectively improves the resistance of plants to biological and non-biotic stress.The total amount of potassium in soil ranges from 0.04% to 3%,but most soil potassium(90-98%)exists in the form of insoluble or insoluble mineral potassium,which cannot be directly absorbed and utilized by plants.At present,in agricultural production,a large amount of industrial potassium fertilizer(such as potassium sulfate and potassium nitrate)is often used to alleviate this problem.However,potassium fertilizer is easily fixed by the soil,becoming ineffective or slow-release potassium,leading to reduced potassium fertilizer utilization rate and resource waste.On the other hand,the production of potassium fertilizer in China is no longer sufficient for consumption,with 50% to 70% of potassium fertilizer relying on imports.Long term and large-scale application of fertilizers not only increases production costs,but also causes serious problems such as soil compaction,salinization,and excessive heavy metals,leading to ecological environment pollution and not conducive to sustainable agricultural development.Therefore,finding new methods to convert mineral potassium into soluble potassium that is easily absorbed and utilized by crops,meeting the growth needs of plants,and achieving the goal of "reducing fertilizer application and increasing efficiency" has become a current research hotspot.Rhizosphere microorganisms are an extremely important component of soil ecosystems,participating in biochemical cycling and energy flow,including nutrient cycling such as carbon,nitrogen,and phosphorus,as well as the decomposition of soil organic matter.Research has shown that plant rhizosphere growth promoting bacteria can decompose insoluble minerals in the soil and convert them into compounds that are easily absorbed by plants,thereby helping to protect plants from nutrient stress,Improve the soil microecological environment.Potash solubilizing bacteria,also known as silicate bacteria,are a kind of rhizosphere microorganisms capable of decomposing insoluble silica aluminate minerals such as potassium feldspar and apatite,which can transform insoluble potassium in soil into soluble forms.Therefore,potassium solubilizing bacteria in soil play a crucial role in the natural potassium cycle.Conducting research on the separation and screening of potassium solubilizing bacteria and the preparation process of bacterial agents,seeking efficient utilization and alternative technologies for potassium fertilizer,is of great practical significance in alleviating the current situation of potassium resource shortage in China,promoting sustainable agricultural development,and reducing the use of fertilizers.In order to screen strains with efficient potassium solubilization ability,this study selected excellent growing plants from the tobacco planting areas of Luzhou and Huangdu in Xuancheng,Sichuan.Two strains with efficient potassium solubilization ability were selected from the rhizosphere soil of tobacco plants.After long-term potassium solubilization ability testing,it was found that the potassium solubilization rates of strains DY211 and WC11 could reach 357.14% and 321.43%,respectively.Genetic evolution analysis was conducted using 16 S r DNA sequences,and the results showed that the potassium solubilizing and promoting bacterial strain DY211 was burkholderia pyrrolifera,while the strain WC11 was a levoglycan producing microbacterium.Further optimization was carried out on the cultivation conditions of potassium solubilizing bacteria.Through single factor and orthogonal optimization experiments,it was found that the optimal potassium solubilization rate was achieved at a culture temperature of 28 ℃,a rotation speed of 160 r/min,an initial p H value of 6.5,and an inoculation amount of 8%.WC11 achieved a potassium solubilization rate of 420%,which was significantly higher than the highest potassium solubilization rate of 347%in the single factor experiment.DY211 achieved a potassium solubilization rate of389%,and it was also significantly higher than the highest potassium solubilization rate of 305% in the single factor experiment.To investigate the growth promoting effects of strains DY211 and WC11 on tobacco,seed germination experiments and pot experiments were designed.The experimental results showed that the D4,D7,W4,and W7 treatment groups had a significant increase in dry weight compared to the blank group,with D7 and W4 performing the best,increasing the dry weight of tobacco seedlings by 214.29% and271.43%,respectively.Through routine chemical composition testing of tobacco seedlings,the content of chlorine,potassium,and nicotine was significantly increased,and the treatment groups D7 and W7 were the best.Further field experiments were conducted to verify the results of the pot experiment.When the tobacco grows to maturity,the biomass of mature tobacco plants is counted and the potassium content in the middle and top leaves is detected.Research has found that the bacterial solution prepared using DY211 and WC11 can increase tobacco biomass.Through data analysis,the potassium content in the middle and top leaves of treatment group D7 showed the most significant increase,with potassium content growth rates reaching22.22% and 72.48%,respectively,and had little impact on tobacco seed emergence;The potassium content in the middle and top leaves of treatment group W1 was 2.38%and 1.56%,respectively,which increased by 46.92% and 43.12% compared to the control group.This study conducted a preliminary exploration of the potassium solubilization mechanism of the selected potassium solubilizing bacteria.By detecting the dynamic changes in p H value in the fermentation broth and detecting the effective potassium content in the fermentation broth,it was found that as the acidity continued to increase,the effective potassium content in the solution continued to increase,ultimately reaching equilibrium.Through the detection of organic acid components in the fermentation broth,the data showed a significant change in citric acid content,while the other organic acids did not show significant changes.Therefore,it is speculated that the potassium feldspar powder is decomposed by the potassium solubilizing bacteria DY211 and WC11 by secreting citric acid.Through scanning electron microscopy observation,it is found that before and after the action of the potassium solubilizing bacteria,the surface of the potassium feldspar powder becomes significantly rough,and the decomposition effect is obvious.