香根草修复三氮苯类除草剂农田土壤污染的根际效应研究

As a principal series of herbicides, trazine herbicide was widely used in cropland in the world especially in China, and the phenyl group with three nitrogen will also be selected in the newly-exploited herbicides. About 80 percent pesticide residues remain in the cropland soil, particularly trazine herbicide has phenyl group with three nitrogen, which could go against degradation by microorganisms, and keep stable in the environment for several years. Those kinds of pollutants have been a threat to the environment and human health through the food chain and bio-accumulation effect. Many of them are environmental endocrine disrupting chemicals with highly toxic and carcinogenic properties. Therefore, the ecological remediation problem of cropland soil polluted by trazine herbicide is one of the urgent tasks in our country. In the remediation of soil polluted by herbicides, herbaceous plants with fibrous deep root system show great potential of phytoremediation, especially the micro-environments around rhizosphere could expedite the mineralization of pesticides. Vetiver has been considered to be an ideal in-situ remediate plant, mainly due to its well-developed root system, strong pollution resistance and rapid environmental adaptiveness and etc. However, rare researches have focused on the rhizosphere effect and its underlying mechanism. This proposal will focus on the performance of rhizosphere of vetiver on the removal of trazine herbicide. Through this proposal, we expect to provide theoretical basis and practice guidance for phytoremediation of trazine herbicide-polluted cropland soils, and help to strengthen the line of defense for human health and food safety.

作为全球除草剂中一个重要的系列，三氮苯类除草剂被广泛应用于农田除草，且三氮苯环结构也将作为新除草剂品种开发的基团。约80%的农药使用后残留农田土壤等环境中。这类除草剂因其化学性质稳定，不易被微生物所降解。通过食物链和生物富集作用，已经对环境及人类健康造成威胁。其中许多品种还是内分泌干扰物质。因此，农田土壤三氮苯类除草剂污染修复是我国农田生态环境的迫切任务之一。在农药土壤污染修复中，须根系深根的草本植物具有较大优势，尤其是根际区的土壤微环境可加速化学农药的矿化。香根草因其根系发达，耐污染能力和环境适应能力强等优势，被广泛运用于污染修复领域。然而，从根际效应及其作用机理方面的研究鲜有报道。本项目拟以三氮苯类除草剂为研究对象，香根草为修复植物，从根际环境和污染物去除的关系进行研究。以期为受三氮苯类除草剂污染的农田土壤修复提供理论依据和实践指导，为人类健康和食品安全加一道防线。

三氮苯类除草剂被广泛应用于农田除草，约80%的农药使用后残留在农田土壤等环境中，通过食物链和生物富集，对环境及人类健康造成威胁。因此，农田土壤三氮苯类除草剂污染修复迫在眉睫。香根草根系发达、耐污力和适应性强，被广泛运用于污染修复领域。本项目以阿特拉津和扑草净为研究对象，香根草为修复植物，温室盆栽模拟为试验方法，从香根草对水体中扑草净胁迫的生理生化响应和去除、香根草对土壤中阿特拉津的吸收及体内和根际降解、阿特拉津和扑草净胁迫下的香根草根系分泌物特征、根际土壤微生物群落结构变化及扑草净降解菌株筛选等方面入手，阐明香根草修复三氮苯类除草剂污染农田土壤的机制。结果表明：（1）香根草可以适应水环境中的扑草净胁迫，并通过根系吸收转移至地上部，促进扑草净去除；（2）香根草能够吸收土壤中的阿特拉津，在体内代谢为羟基阿特拉津、脱乙基阿特拉津、脱异丙基阿特拉津和脱乙基脱异丙基阿特拉津，4种产物均为香根草体内第一次鉴定到；（3）种植香根草使根际土中阿特拉津的去除率显著提高12.37%，香根草增强了阿特拉津的脱烷基降解途径；（4）分别在阿特拉津和扑草净胁迫的香根草根系分泌物中检测到83种和40余种化合物，这些物质可能改善了根际的pH值、水溶性有机碳和铵态氮含量以及土壤酶活性等关键土壤性质，刺激微生物生长，从而促进阿特拉津降解；（5）香根草明显促进土壤中Arthrobacter和Bradyrhizobium属以及根际土中Rhodococcus和Nocardioides属细菌的生长，这些细菌可能是阿特拉津降解的主要贡献者；（6）筛选出两株细菌枯草芽孢杆菌和腐生性葡萄球菌，对扑草净的降解效率分别为67.70%和61.20%。研究结果为三氮苯类农药和根系分泌物的测定技术提供参考，为三氮苯类农药降解微生物筛选和运用指明了方向，也为香根草-微生物联合修复三氮苯类农药污染土壤技术提供理论依据。本研究的基础资料可促进生态学、环境科学、植物营养学、植物生理学和微生物学等相关学科领域的交叉融合，为土壤农药污染研究工作提供有益借鉴。同时，研究成果为我国农药污染土壤的环境治理提供重要的理论支撑，对人类健康和环境污染治理具有重要的理论意义和现实意义。