Study On Phosphorus Dissolving Mechanisms And Growth-promoting Effects Of Affinity Phosphate-solubilizing Rhizobacteria For Wheat

In order to study the phosphorus dissolving mechanisms and growth-promoting effectsof affinity phosphate-solubilizing bacteria?PSB?for wheat,27 PSB with specific affinity for wheat,which isolated from wheat rhizosphere by double-screening method of selective culture medium and wheat lectin by our laboratory were applied as research materials in this study.The phosphate solubilization ability of these strains for inorganic phosphorus and organic phosphorus was determined.A total of 5 strains with different phosphorus-solubilizing ability were selected to study their phosphate-solubilizing mechanisms in physiological and biochemical level and molecular level,respectively.Furthermore,Root bag test was applied to study the effects of PSB on the wheat seedling growth and root development,and pot experiments were conducted to study the effects of 2 excellent affinity PSB and their different concentrations ratios on wheat growth,phosphorus uptake,and soil available phosphorus content.The results will provide basis for the study of mechanism of phosphate solubilizing of PSB and plant response for it.PSB were cultured in inorganic phosphate?Ca₃?PO₄?₂ and CaHPO₄·2H₂O?medium and organic phosphate?phytate?medium,respectively.The content of soluble phosphorus in the broth was detected.A total of 5 PSB?P1616,WS32,P16,P17 and WS33?with a large difference in phosphate-solubilizing abilities were selected to study the phosphorus dissolving mechanisms.The strain WS32 had better ability to dissolve Ca₃?PO₄?₂,strain P1616 had better ability to dissolve CaHPO₄·2H₂O and phytate,and strain WS33?P17 and P16 had worse ability in dissolving organic and inorganic phosphorus.Strain P1616,WS32,P16,P17 and WS33 were cultured in Ca₃?PO₄?₂ and phytatemedium respectively.The soluble phosphorus content and the pH in culture liquid were measured every day.The results showed that strain WS32 had the highest ability to dissolve Ca₃?PO₄?₂,followed by strain P1616,while the pH in culture liquid of strain WS32 had the largest decrease,followed by strain P1616.The results showed that the ability of bacteria to dissolve Ca₃?PO₄?₂ may be related to its acid production.Strains P1616 had the highest ability to solve phytate,followed by strain WS32,but the results showed that the ability of bacteria to dissolve phytate had no significant correlation with the pH in culture liquid.The type and content of organic acids produced by 5 PSB in Ca₃?PO₄?₂ medium weredetected by HPLC.The phosphatase activity of the strains in phytate medium was determined by the method of p-nitrophenyl phosphate.The results showed that the total organic acids produced by strains P1616 and WS32 were higher than P16,P17,and WS33in species and yield.The enzyme activities of phosphatase secreted by strains P1616 and WS32 were higher than that of strains P16,P17 and WS33.The results that amount of organic acid and phosphatase secreted was positively correlated with the ability of the strain to dissolve phosphorus showed that the inorganic phosphorus dissolving mechanism of PSB may be that PSB can produce various types of organic acids to dissolve insoluble inorganic phosphorus into soluble phosphorus;The mechanism of PSB to dissolve insoluble organic phosphorus is may be that PBS can produce phosphatase for dissolving insoluble organic phosphorus into soluble phosphorus.Phosphorus dissolving mechanisms of strains was studied in physiological and biochemical levels.Effects of 5 PSB on expression levels of phosphorus transport protein TaPT4 gene and auxin-binding protein TaABP1gene were determined by quantitative reverse-transcription PCR method.TaPT4 gene,a phosphorus deficiency indicator gene,showed a significant increase in expression level under low phosphorus treatment.This can be used to determine the level of phosphorus in the environment.The experiments results showed that5 PSB down-regulated the TaPT4 gene expression level in wheat roots,indicating that 5PSB can dissolve insoluble phosphorus in the soil and increase the content of available phosphorus in the rhizosphere soil of wheat for plant absorption and utilization.Meanwhile,the 5 PSB effectively up-regulated the TaABP1 gene expression level in wheat roots,which indicated that the PSB can promote the growth of wheat by up-regulating TaABP1 gene expression.The results revealed mechanisms of phosphorus dissolving and growth promotion for PSB in molecular level.The effects of 5 strains on the growth and root development of wheat was measured by the root-bag test.The results showed that these 5 PSB can promote the total root length,projected area,surface area,total volume,tips,forks and crossings of wheat root.At the same time,the dry weight,fresh weight and plant height of wheat can also be increased by these PSB.Strain P1616 and WS32 are superior to strains P16,P17 and WS33in promoting the growth and root development of wheat.Two excellent affinity PSB WS32 and P1616 were selected as the research materials in pot experiment.The effects of strain WS32,strain P1616 and Different concentration ratios?bacteria liquid volume ratios of WS32 and P1616 were 2:1,1:1and 1:2,respectively?of these two strains on wheat growth were investigated.The results showed that the two strains and mixed strains can all increase the dry weight,fresh weight and plant height of wheat,and increase the phosphorus content and phosphorus content in wheat plants.The effects of mixed strains were better than that of a single strain.Among which the height,fresh weight,dry weight,plant total phosphorus content and soil available phosphorus content in wheat plant inoculated by mixed strains with 2:1 volume ratio of WS32 and P1616 were increased by 15.62%,8.92%,19.34%,49.69%and 11.98%,respectively,compared with the uninoculated ones.