Study On The Mechanism Of Controlling Red Soil Pest And Chromium Pollution By Biochar-fungi Complex

Underground pests and heavy metal pollution have been important problems of red soil in southwest China for a long time.Based on the special physical and chemical properties of red soil,the control effect of traditional methods can not reach the expectation.In order to enhance the stability and virulence of the use of biocontrol fungi,the biochar complex was prepared by loading Beauveria bassiana spores with biochar as the carrier.It was proved that the biochar complex can improve the function of Beauveria bassiana and the mechanism of the enhancement of virulence and activity was analyzed from the genetic level.On this basis,in order to enable functional fungi to efficiently recover heavy metal chromium elements,chrome-resistant Aspergillus niger was screened from chrome-polluted red soil,and biochar complex was prepared using biochar as the carrier.The adsorption capacity and adsorption mechanism of biochar complex were explored.The specific results obtained from the above work are as follows:1.The Beauveria bassiana Bb0816 strain was isolated and purified from Cylas formicarius infected in Yunnan Province.Using tobacco varieties K326 and Hongda as source hosts,the bioassay was carried out by immersion method.The time-dose-mortality model was used to analyze the time and dose effects of infection and disease.The results showed that Beauveria bassiana Bb0816 strain had strong infection and pathogenicity against both Hongda and K326 tobacco varieties.2.A1 strain was isolated and screened from red soil heavily polluted by chromium in Yunnan Province,China.It was identified as Aspergillus niger by 18S r RNA sequencing.The adsorption effect and mechanism of A1 strain on chromium in red soil were studied in laboratory.The results showed that A1 strain of Aspergillus niger had strong chromium tolerance and adsorption capacity.The adsorption of chromium by A1 strain was mainly accomplished through intracellular metabolism and surface adsorption.The surface adsorption depends on the complexation of functional groups such as-C=C-,-OH,-NH₂,-C=O on the surface of Aspergillus niger cells and the formation of stable coordination compounds.Compared with exogenous microbial agent inoculation,the content of Cr⁶⁺in red soil contaminated with chromium decreased significantly after inoculation with A1,and the high toxicity forms（water-soluble and exchange states）decreased,while the low toxicity forms（precipitated and residual states）increased.3.The carrier biochar was prepared from corn straw,the results showed that with the temperature increasing from 300℃to 600℃,the carbonization degree of biochar was deepened,the specific surface area was increased significantly,and the average pore diameter,surface functional groups and the contents of O and H elements were decreased significantly.The polarity,hydrophilicity and abundance of oxygen-containing functional groups of biochar can be significantly improved by metal salt modification,and uniform active sites can be formed on the surface of biochar.Combined with fungal spore characteristics,the biochar prepared at 500℃has better carrier performance.4.The adsorption capacity of B.bassiana spores at 500BC reached 9.5971×10⁵conidia/g.The adsorption process of spores was in line with the quasi second-order kinetic equation.After stable adhesion,the carbon complex can reach the desorption capacity of 6.1406×10⁵ conidia/g at 30℃.The adsorption capacity of 500BC was further improved to 13.0380×10⁵ conidia/g by premodification with ferric sulfate.The chemisorption of the carboniferous complex was mainly completed by the amide group,amino group,nitro group and unsaturated carbon and nitrogen bonds on the surface of biochar,while the physical adsorption was mainly completed by steric hindrance effect and pore effect.The study proved that biochar is an excellent carrier of fungal spores,which can realize the fixation of fungal spores by using its abundant pore structure and functional groups,providing a new idea for the preparation of new dosage forms of biopesticides.5.The formation of 500BC-Beauveria bassiana complex using biochar as carrier could greatly improve the storage of conidia at room temperature and the functional preservation ability of strains under high temperature and ultraviolet stress,and significantly improve the virulence of Beauveria bassiana in red soil The enhancement of complex function was related to the enhancement of host wall adhesion and gene expression after biochar loading..In addition,carbon bacteria complex can significantly improve the dominance of Beauveria bassiana and ensure the diversity of fungi in red soil.The formation of 500BC-Beauveria bassiana complex solves the three major problems of unstable effect,high preservation difficulty and great environmental impact during the use of biopesticides.By using biochar as the carrier,the efficacy and niche competitiveness of Beauveria bassiana in red soil are comprehensively improved,and the formulation of biopesticides and added value of biopesticides are improved.It provides a new working mode for the extension of biopesticide.6.Biochar loading can greatly improve the activity and stress resistance of Aspergillus niger.So that the fungal adsorbent can exert the efficient adsorption capacity of chromium element and the driving ability of sexual transformation,and at the same time has the characteristics of recycling.The biochar-Aspergillus niger complex can complete the detoxification of chromium through intracellular metabolism and surface adsorption,in which the intracellular metabolism of Aspergillus niger components is the main detoxification mechanism.Aspergillus niger can change the transport of metal ions and surface macromolecules by changing the membrane channel permeability,transmembrane protein structure（ABC transmembrane protein）and sporulation behavior.At the same time,by increasing the synthesis of pyruvate,aldehydes,acetyl groups,sulfur-containing amino acids and a large number of reducing sugars,the reduction detoxification and intracellular binding of chromium ions are completed.In addition,the using of 300BC-Aspergillus niger complex can significantly improve the leaching structure and element retention capacity of surface red soil,and can significantly increase the abundance of Aspergillus niger and the diversity of fungi in red soil.The successful use of Biochar-Aspergillus niger complex can provide a new green,safe and efficient way for the treatment of heavy metal pollution in red soil.In conclusion,the Beauveria bassiana complex prepared in this paper has good functionality and stability,which can better control underground pests.Meanwhile,the Aspergillus niger complex can not only drive the conversion of chromium into low-toxicity form,but also reduce the heavy metal chromium through recycling.The preparation of biochar-fungi complex further broadens the application scenarios of biocontrol bacteria and fungal adsorbents and has strong practical significance.