The Degradation And Ecological Effect Of Polyoxin In Tobacco-ecosystems

Polyoxin is a wide spectrum antibiotic bacteriostat, it is a lowtoxic bacteriostat, the widely use of it in tobacco production have inevitably a negative impact on ecosystem and human health. This article systemic study the residue and degradation of polyoxin in tobacco field ecosystem and microecology.The research focus on studying the the residue and degradation of polyoxin in tobacco field ecosystem, learning about its degradation and residues on tobacco leaves and in soil as well as the influence of polyoxin in the population size and structure of microorganism and soil enzymes. Then we also study the transferring of polyoxin in the tobacco field ecosystem.these can help us understand the effects of polyoxin on tobacco field ecological environment so as to provide the technical guidance in safe and proper use of antibiotic pesticides in tobacco production. Main conclusions:(1) We use high performance liquid chromatography to analysis the residues of polyoxin in tobacco planting soil and tobacco plants, the rate of addition recovery of polyoxin and relative standard deviations are in the allow range of guidelines in pesticide residues test. When the mass fraction of polyoxin in fresh tobacco, dry tobacco and the blank samples of tobacco planting soil respectively is0.06, and0.60, and1.00mg/kg,the average rate of addition recovery of polyoxin range from91.64%to98.32%, relative standard deviation range from0.97%to5.93%; the minimum detection volume of polyoxin is1.0×10-9g, the minimum detection concentration in tobacco planting soil, fresh tobacco and dry tobacco is0.05mg/kg. The Sensitivity and accuracy of this method meet the technical requirements for pesticide residue detection, so it is useful in the actual work.(2) We have conducted the experiment to study the residual of polyoxin in tobacco planting field in Changsha Hunan province. The results indicate that digestion process of polyoxin in tobacco planted observe the level1reaction kinetics equation and It is a gradually reduced process, the digestion rate in fresh tobacco leaves more faster than in the tobacco planting soil,the digestion half-life of polyoxin in tobacco planted soil is10.34d compared to4.98d in fresh tobacco leaves. (3) We use water(water consumption is50kg per Mu)to dilute3.5%polyoxin in water solution in order to reach the effective components concertration of67.2g/ha and100.8g/ha then spray2times and3times respectively, the interval of application is every7days. The residues volume in the tobacco planted soil range from LOD(less than0.05mg/kg) to0.132mg/kg at the time of7d after the last application, It range from LOD to0.071mg/kg after14d, and it is just LOD after21d. polyoxin can not be detected in dry tobacco leaves,probably influence by its physical and chemical properties and high temperature during the tobacco Flue-curing process. polyoxin may be volatiled and high temperature degraded during tobacco Flue-curing process,resulting in not being detected(4) Polyoxin have a certain degree effect on the activity of polyphenol oxidase,catalase and urease,its impact is different from different concentrations in general effects of low concentrations are less than high-concentration, the effect will weaken as the time passed by and finally came back to its normal level.(5) Polyoxin also have certain degree effect on population number of bacteria and fungi in tobacco planting soils. The impact of polyoxin on the number of bacteria and fungi is greater under high concentration compare to low concentration. polyoxin have a role in stimulating soil microorganisms growth after the suppression, but with the extended test time, soil microorganisms will eventually be restored to the control level, It suggests that polyoxin have not a real harm to soil microorganisms(6) Polyoxin can be transfer from soil to tobacco plants in the "soil-tobacco plants" system. The changing trends of transferred volume are first increase and then decrease with the time extending. It can also transfer between different tobacco leaves from different parts of tobacco plants, the transferred volume from middle part of tobacco leaves to up part as well as to down part of tobacco leaves first increase and then decrease what’ more,the transferred volume to up part is more that the down part.