Study On Straw Biochar Coupled Functional Microorganisms For Enhanced Atrazine Removal And Phosphorus Solubilization Ability In Soil

China,as a major agricultural country,has made great achievements in agricultural development.However,in order to ensure the production of grain,the unreasonable use of pesticides in the process of agricultural development has caused pesticide residues in farmland soil and insufficient supply of land nutrients,which seriously affects the sustainable development of agriculture.Atrazine is a common triazine herbicide with relatively stable chemical properties in the soil,which can cause stubble obstacles and has long residues and biological toxicity.Phosphorus is an essential nutrient element for crop growth,but crop yields are often limited because of the low availability of phosphorus in the soil.Bioremediation has gradually become the main way to remove atrazine from the environment due to its complete degradation and simple operation.However,some environmental variables in contaminated soil could easily cause some functional bacteria to lose their activity.Biochar as a low-cost and stable substance,its surface characteristics and porous structure could provide a good living environment for microorganisms,and then enable microorganisms to perform their maximum functions.In this study,agricultural waste corn stover was used to prepare low-cost biochar materials,coupled with atrazine-degrading bacteria Acinetobacter lwoffii DNS32 and phosphate-solubilizing bacteria（PSB）,which can effectively improve the level of soil phosphorus while reducing the pollution level of atrazine.The main findings of the study are as follows:（1）Three kinds of biochar（BC250,BC550,and BC850）with different pyrolysis temperatures（250℃,550℃,and 850℃）were characterized by scanning electron microscopy（SEM）,specific surface area（BET）,and fourier transform infrared spectroscopy（FTIR）.The results of SEM showed that with the increase of the pyrolysis temperature of biochar,the richer of the microporous structure.The results of BET showed that with the increase of the pyrolysis temperature of biochar,the larger of specific surface area and pore volume,the smaller of average pore diameter.The results of FTIR showed that with the increase of the pyrolysis temperature of biochar,the number of functional groups decreases,the polarity of biochar weakens,and the the degree of aromatization increases.The adsorption kinetics of atrazine on the three types of biochar were conforms to the pseudo-second-order kinetic model.The results of adsorption isotherms showed that BC250 was more suitable for Freundlich model,BC550 and BC850 were more suitable Langmuir model.（2）BC250,BC550,and BC850 had different effects on PSB.BC550 could obviously promote the growth of PSB,it significantly improved the phosphorus solubilization ability,indoleacetic acid production,growth capacity,acid phosphatase activity,and biofilm forming ability of PSB.The main reason was that the porous structure and surface characteristics of BC550,were more suitable for microorganisms survival and reproduction.while BC850 with a high degree of carbonization,low hydrophilicity and high hydrophobicity surface were not conducive to the growth and survival for microorganisms.（3）The mechanism of BC550 and TPSB（the complex microorganisms of four strains for phosphate-solubilizing bacteria）in the remediation of atrazine pollution by strain DNS32 was revealed.TPSB could use the intermediate metabolites produced during the degradation of atrazine by strain DNS32 as a nitrogen source for growth.Meanwhile,TPSB could secrete low molecular weight organic acids to promote the growth of strain DNS32.The presence of BC550 could promote the production of low molecular weight organic acids and adjust the pH of the culture medium,then provide a more suitable living environment for the strain.Biochar coupled with phosphorus solubilizing bacteria and degrading bacteria DNS32（BC/PSB/DNS32）significantly improved the degradation capacity of atrazine and the expression of the atrazine-degrading genes trzN,atzB,and atzC.（4）The application of BC/PSB/DNS32 could reduce the pollution level of atrazine and improve the level of soil phosphorus.The results showed that at day 3,BC/PSB/DNS32 was added to the contaminated soil with atrazine concentration of 20 mg·kg^-1,the concentration of atrazine remained in the soil was 1.92 mg·kg^-1 compared with soil with only added strain DNS32,the removal rate was increased by 27%.Compared with the soil blank,the available phosphorus content increased by 22.82 mg·kg^-1.This study will contribute to a better understanding of the stimulation strategy of biochar coupled functional microorganisms to enhance the ability to remove atrazine pollution and soil nutrient.