Screening Of Phosphate Solubilizing Bacteria And Its Applications In Tobacco And Corn Planting

Phosphorus is one of the essential nutrient elements for crop growth.When P fertilizer is applied,only about 5%?10%is utilized by crops,coupled with the subsequent use of utilization is not more than 25%,and most is converted biologically unavailable P,resulting in a large amount of phosphorus pool in the soil.Phosphate solubilizing bacteria(PSB)in the crop rhizosphere can convert biologically unavailable P into available phosphorus,which can be directly absorbed by crops,thus as they have a number of applications in agriculture.This study aimed to identify a highly efficient a PSB strain identified Bacillus amyloliquefaciens L5 from maize rhizosphere soil,survey its phosphate solubilizing characteristics,optimize fermentation process,and comparatively evaluate their applications in com and tobacco at a small scale with laboratory available strains(Pseudomonas putida L13 and Bacillus megatherium Z6).This study provides a foundation for the further development of large scale applications of PSB in agriculture.A highly efficient strain,B.amyloliquefaciens L5 for organic and inorganic insoluble phosphorus solubilization,was isolated from the rhizosphere of corn with insoluble phosphate as the sole phosphorus source,which had the ability of calcium phosphate solubilization 554.06 mg/L and phytate solubilization 566.33 mg/L.Further investigation showed that B.amyloliquefaciens L5 was able to secret organic acids,and growth substance in the PKO liquid medium.The major results were:(i)a good correlation between the variable of phosphate solibilizing and cell growth;(ii)phytase was produced mainly in the logarithm growing period;(iii)more than organic acids were detected in the fermentation liquid,mainly lauric acid,propionic acid,butyric acid and acetic acid;(iv)L5 also simultaneously secreted indole acetic acid(IAA)and siderphore;and(v)B.amyloliquefaciens L5 of insoluble phosphorus dissolved in the early and mid growth stage with phytase and organic acid exudation,in the mid to late with cell autolysis also to extracellular release part of the soluble phosphorus.In order to improve the B.amyloliquefaciens L5 spore production,the fermentation medium and culture conditions were optimized,and the optimized medium is:molasses 15 g/L,yeast extract 10 g/L,soybean meal 10 g/L,NaCl 3 g/L,K2HPO4 1 g/L,CaCO3 2 g/L;fermentation temperature is 37 ?,the inoculum age 10 h,initial pH 7.0,2%inoculation amount,loading volume of liquid 20 mL/250mL.The optimized L5 spore yield reached 141.33 × 108 CFU/mL,9.2 times more than the initial medium,and the spore formation rate reached more than 90%.We also conducted solid fertilizer carrier experiments with L5 and other two PSB strains(L13 and Z6),showing the best carrier was peat for L5 and Z6 after 90-d inspection.In the greenhouse,the effects of phosphorus fertilizer of L5,L13,and Z6 and collocation compound fertilizer on maize planting were:(i)the colonization of bacteria was decreased all the time with(6.21?44.28)× 104 CFU/g at the mature period;(ii)it could significantly improve the stem at the mature period with the maximum value increased by 17.25%;(iii)corn starch,protein,cubes,the total sugar and reducing sugar increased by 21.04%,15.24%,11.82%and 27.27%,respectively compared to the control;(iv)the content of available phosphorus was increased to 1.5?11.5 mg/kg at the beginning and then decreased after 50 days of inoculation;(v)in maize rhizosphere soil,the content of IAA and siderophore significant increased compared to the control;and(vi)the P utilization rate by maize plants increased 16.18%,24.89%,22.22%via L13,L5,and Z6 fertilizer applications,respectively.The above data showed that PSB had a good colonization in maize rhizosphere,it could promote maize growth,improve the quality of maize and the utilization rate of phosphate fertilizer,and B.amyloliquefaciens L5 and B.megaterium Z6 had similar effects,which were better than those of P.putida L13.We also further investigated the effect of phosphorus fertilizer(L5,L13,Z6,and special fertilizer)applications on tobacco planting.Our results showed that:(i)phosphorus fertilizer could significantly improve the maturity of tobacco plant height,maximum leaf length,and stem girth by 21.30%,14.81%,and 23.19%,respectively,in the maturity period,the content of total sugar,reducing sugar and total nitrogen increased 11.01%,14.96%,and 11.80%,respectively compared to CK;(iii)it significantly improved the content of available phosphorus in tobacco rhizosphere soil,and available phosphorus increased by 20.85?37.65 mg/kg during the growth period;(iv)it significantly improved the total phosphorus content in tobacco leaf maturity with the highest total phosphorus content increased to 2.02 ‰ from 1.77‰ for CK,approximately a 14%increase;and(v)the yield of tobacco increased by by 3.5%?6.9%,and the outcome value improved 9.8%?13.5%compared to CK.Comprehensively considered,PSB can promote the growth,quality and production output of tobacco,the results was almost same:the combination of B.amyloliquefaciens L5 and B.megaterium Z6 fertilizer and tobacco specific had similar effects,which were better than those of P.putida L13.