塔里木盆地土著细菌Bacillus sp.对氟乐灵降解机理研究

Abstract: Trifluralin largely existed in the cotton soil of Tarim Basin, and had seriously hapered the development of cotton productivity in South of XinJiang. In recent years, many reseachers focused on the importance of the Technology of soil pollution remediation, however, it is few to study the remediation of trifluralin in cotton soil. The project team members had conducted the direct screening method to obtain the Bacillus(ID code:D8) had significant effect in the degradation of trifluralin. This project intends to study further based on the previous research, the growth rhythem of Bacillus and the degradation factors are applied, optimize the degradation conditions and figure out the degradation property of Bacillus; analyse the UV-Vis and GC-MS spectra of trifluralin before and after degradation, find out the degradation pathway of Bacillus and make sure the mechanism between degradation bacteria and trifluralin. The consecutive cultivating cotton land would be choosed as the experimental field, trifluralin is selected as the pollution in the cotton soil, to determine the colonization rule of the strain D8 in the cotton soil, study the number and activity of the strain D8 under the influence of inoculation size,field capacity and fertilizer addition; the research of the interaction between the plant root exudates, the root symbiotic bacteria, soil organic matter and trifluralin, trifluralin degradation bacteria is applied, reveal the mechanism of efficiency influence between the cotton rhizosphere and the trifluralin degradation bacteria.

氟乐灵大量存在于环塔里木盆地棉田土壤中，已严重制约南疆棉花的持续高产和稳产。土壤污染修复技术近年来在国内外受到越来越多的重视，但目前新疆棉田氟乐灵残留对土壤污染的修复研究还处于空白。本课题组前期采用直接筛选法，得到初步鉴定为芽孢杆菌（编号为D8）的菌株对氟乐灵有显著降解作用。本项目拟通过研究D8的生长规律及其降解的影响因素来优化降解条件，明确该菌株的降解特性；通过降解前后氟乐灵UV-Vis和GC-MS图谱分析，确定该菌对氟乐灵的降解途径，揭示降解菌对氟乐灵的作用机理；在南疆连作棉田采集以氟乐灵为目标的污染物，通过接种量、田间持水量、肥料添加量对降解菌株D8数量和活性影响的研究，确定D8在棉田土壤的定殖规律；研究棉花根系分泌物、根系共生菌和土壤有机质同氟乐灵和D8的相互作用，揭示棉花根际环境对土壤中氟乐灵降解菌有效性的影响机理，为氟乐灵污染土壤的修复技术提供理论依据。

氟乐灵（trifluralin）作为二硝基苯胺类除草剂，在棉田、稻田等作物一年生杂草防治过程中得到广泛应用，但由于其使用时间长，在土层中半衰期长，在棉田自然环境中降解缓慢，连年积累使下茬棉苗产生茎基部膨大、维管束中空而干枯死苗，给棉花生产带来严重影响。为解决氟乐灵残留污染造成的药害问题，本研究进行了氟乐灵降解菌的筛选、鉴定和降解机理研究，主要研究内容如下：.（1）我们从常年施用氟乐灵的棉田土壤取样，对土壤样品进行驯化、富集培养和筛选培养，筛选出1株长势良好具有氟乐灵降解潜力的菌株，通过菌落形态学观察、电子显微镜菌体形态观察、生理生化试验鉴定初步确定降解菌 D8为为蜡样芽孢杆菌(Bacillus cereus)。 .（2）以连作15年以上棉田土壤为材料，采用直接稀释涂布法分离得到1株能够降解氟乐灵的细菌D8(Bacillus cereus)，通过单因素实验研究降解特性。在氟乐灵质量浓度为50 mg/L、接种量为4%、外加氮源酵母浸粉0.1%、温度37 ℃、pH 5.0条件下，接种3 d后对氟乐灵降解率达到59.89%以上。 .（3）通过离体实验，采用液质分析，终降解产物为2-乙基-4-硝基-6-三氟甲基-苯并咪唑（C10 H8 F3 N3 O2）和3-硝基-5-三氟甲基苯胺（C7H5F3N2O2），分析了降解菌作用氟乐灵使其脱烷基、去硝基化的降解机理。.（4）将降解菌 D8接种到 50 mg/kg 氟乐灵毒土中，接种量为4%、外加氮源酵母浸粉0.1%、温度37℃ 、pH值5.0条件下，接种10 d 可解除了残留氟乐灵对反枝苋生长的威胁。.（5）为了解降解菌 D8 对棉苗药害缓解作用，在大田进行小区试验，调查结果表明在棉苗移栽前 20 d 接种降解菌D8处理组能够有效缓解氟乐灵药害，移栽后 60 d 药害缓解率可达 70%以上；移栽后再将降解菌 D8 接种到土壤中的处理，在一定程度能够缓解氟乐灵药害，降低氟乐灵药害抑制率，移栽后 60 d 药害缓解率在 40%左右，因此我们应当在棉苗移栽前进行土壤处理以最大限度减轻氟乐灵残留对棉苗生长的影响。