A Study On The Phosphorus Solubilizing Characteristics And Lead Immobilization Capacity By Penicillium Aurantiogriseum

Phosphorus（P）is one of the most important nutrients essential for plant growth and development,and plays an important role in enhancing the environmental stress resistance of crops and promoting fruit growth and development.Soil phosphorus exists mainly in the form of insoluble phosphate,which is difficult for crops to absorb and use directly.The application of phosphorus fertilizer can alleviate the problem of insufficient effective phosphorus during crop growth and development,but the phosphorus applied to the soil is easily combined with Ca²⁺,Fe³⁺and other metal ions to form insoluble phosphate.In addition,the massive application of phosphate fertilizer will also intensify the depletion of phosphate resources,increase the accumulation of soil phosphorus and increase the risk of environmental pollution.Therefore,improving the conversion of insoluble phosphate in soil to a form of phosphorus that can be directly absorbed and used by plants is a potentially effective measure to improve crop yields and alleviate the phosphorus resource crisis.Phosphorus-solubilizing microorganisms can effectively promote the transformation of insoluble phosphorus in soil to plant absorbable forms.Low molecular weight organic acids secreted by phosphorus-solubilizing microorganisms can not only significantly reduce environmental p H,but also complex with Ca²⁺,Fe³⁺and other metal ions to promote the release of phosphorus in insoluble phosphates.Compared with phosphate-solubilizing bacteria and phosphate-solubilizing actinomycetes,phosphate-solubilizing fungi have stronger phosphate-solubilizing ability,and their phosphate-solubilizing ability can still be maintained after subculture.Oxalic acid is the main organic acid secreted by phosphate-solubilizing fungi,which can not only effectively promote the release of phosphorus in insoluble phosphates,but also combine with heavy metal ions such as lead to insoluble lead oxalate precipitation.Therefore,phosphate-solubilizing fungi are also often used for remediation of lead pollution.Tricarboxylic acid cycle（TCA cycle）is the only pathway for phosphate-solubilizing fungi to secrete oxalic acid.Oxaloacetate acetyl hydrolase（OAH）cleaves oxaloacetate to oxalic acid and acetic acid during TCA cycle.While the activation of OAH enzyme is related to Mn²⁺,therefore,the concentration of Mn²⁺is a critical factor affecting the secretion of oxalic acid in phosphate solubilizing fungi.In addition,the ability of phosphate solubilizing fungi to secrete organic acids is influenced by many environmental factors such as environmental p H,carbon,nitrogen and phosphorus sources.Therefore,it is of great theoretical and practical significance to clarify the characteristics and mechanisms of the effects of different environmental factors on the phosphorus solubilizing ability of phosphorus solubilizing fungi to improve the effectiveness of soil phosphorus and achieve efficient phosphorus solubilization and lead fixation by phosphorus solubilizing fungi.In this study,Penicillium aurantiogriseum,a phosphorus-solubilizing fungus with high phosphorus-solubilizing ability,was used as the test strain.To investigate the effect of different carbon,nitrogen and phosphorus sources on their organic acid secretion and phosphorus solubilization capacity.The tolerance of the strain to high concentrations of lead and the effect of different Mn concentrations on its organic acid secretion and lead fixation capacity were also investigated.The article specifically examines the following3 areas.1.Differences in the phosphorus solubilization capacity of Penicillium aurantiogriseum under different nutrient conditionsThe effects of different carbon sources（glucose,sucrose and starch）and nitrogen sources（ammonium nitrogen,nitrate nitrogen and urea）on the phosphorus solubilization capacity of a typical phosphorus solubilizing fungus,Penicillium aurantiogriseum,were investigated.The results showed that ammonium nitrogen（（NH₄）₂SO₄）and sucrose could significantly increase the phosphorus solubilization ability of Penicillium aurantiogriseum,with the highest phosphorus release of 1000 mg/L.The effect of carbon source on the phosphorus solubilization ability of Penicillium aurantiogriseum was not significant,while nitrate nitrogen and urea significantly inhibited the phosphorus solubilization ability of Penicillium aurantiogriseum,with the phosphorus release of only about 760 mg/L.In addition,glucose and ammonium nitrogen can promote the secretion of organic acids by Penicillium aureum,the most important of which is oxalic acid,with a secretion amount of 260 mg/L.XRD results indicate that oxalic acid secreted by Penicillium aureum dominates the release of phosphorus from tricalcium phosphate and forms a large amount of calcium oxalate（Ca C₂O₄）minerals.This paper has shown that increasing the phosphorus release capacity of Penicillium aurantiogriseum requires increased input of ammonium nitrogen.This study elucidates the phosphorus solubilization characteristics of Penicillium aurantiogriseum under different nutrient conditions,and provides a theoretical basis for its use in activating insoluble soil calcium phosphate salts.2.Study on the ability of Penicillium aurantiogriseum to release phosphorus from different insoluble phosphatesIn this chapter,based on the previous study on the phosphate-solubilizing characteristics of Penicillium aurantiogriseum,the dissolution ability of Penicillium aurantiogriseum to different insoluble phosphates was explored.Calcium phosphate（Ca₃（PO₄）₂）,iron phosphate（Fe PO₄）and aluminum phosphate（Al PO4）were selected as insoluble phosphate.The results showed that P.cinerea had the highest phosphorus release amount of 950 mg/L for tricalcium phosphate.The phosphorus release of iron phosphate and aluminum phosphate were only 114 mg/L and 185 mg/L,respectively.In addition,the highest oxalic acid secretion was 253 mg/L when P.cinerea dissolved tricalcium phosphate.XRD results showed that oxalic acid had the strongest binding ability with Ca²⁺,and the formation of a large amount of calcium oxalate（Ca C₂O₄）could further promote the release of phosphate phosphorus.This study showed that Penicillium aurantiogriseum had the strongest activation ability for tricalcium phosphate,which laid the foundation for its dissolution of insoluble calcium phosphate in soil.3.Effect of different concentrations of Mn²⁺on the lead fixation capacity of Penicillium aurantiogriseumIn this chapter,the effects of different concentrations of Mn²⁺on the oxalic acid secretion and lead fixation capacity of Penicillium aurantiogriseum were studied to investigate the changes in the removal rate of Pb²⁺from aqueous systems and the transformation process of lead forms.The results showed that Penicillium aurantiogriseum was able to tolerate high Pb toxicity and still survive under 1000 mg/L Pb concentration.The low concentration of Mn²⁺（3.75 mg/L）increased the removal rate of Pb ions（98%）,while the high concentration of Mn²⁺（15 mg/L）significantly inhibited the removal rate of Pb ions（70-80%）.In addition,the high concentration of Mn²⁺significantly reduced the effective Pb content in the precipitation（22 mg/L）compared to the low concentration of Mn²⁺treatment.This study shows that Penicillium aurantiogriseum is feasible for the application of lead contamination remediation,and the low concentration of Mn²⁺can promote the release of oxalic acid by Penicillium aurantiogriseum and enhance the removal of lead by Penicillium aurantiogriseum.