环境中过量氮素对手性除草剂赋存特征及其生态毒性效应影响机制

Nowadays, fertilizers and pesticides, the main two driving factors for the promotion of the grain yield, have aroused tremendous influence on environmental quality. When the increase of pesticide residue comes across to excessive nitrogen, the eco-toxicity effects of widely-use pesticides are bound to face a synergistic effect caused by nitrogen surplus except for the structural effect. This subject will establish controllable aquatic and terrestrial experiment models based on simulation of farmland soil and surface water. Three typical chiral herbicides are set as the research objects to investigate the degradation and transportation of chiral herbicides in soils under excessive nitrogen background. Also, Arabidopsis thaliana, non-target beneficial plant Oryza. Sativa L. and non-target harmful plant Cyanobacteria are chosen as model organisms to detect the effect of excessive nitrogen on chiral herbicide enantioselectivities from the aspects of growth influence, oxidant damage and algal toxin release. In addition, we will use carbon and nitrogen stable isotope technology, combining regular analytical methods to better understand the migration and conversion of chiral herbicides and nitrogen metabolism process, and reveal the molecular mechanism of the change of chiral herbicide eco-toxicity enantioselectivities with excessive nitrogen. This study is not only expected to help make proper usage of chiral herbicides when eutrophication occurs, but also to provide more accurate predication and more objective assessment for environmental safety.

目前，我国粮食产量增加的两大驱动因子(化肥和农药)已显著影响环境质量而成为热点问题。当这两大问题不期而遇，两者间的相互作用不可小觑。因此，农药环境生态毒性效应研究中，除了关注污染物本身结构差异外，过量氮素的协同影响也不容忽视。本课题将模拟农田土壤和地表水体，构建室内可控的陆生和水生两种实验模式，选用三种（类）典型手性除草剂，研究除草剂在过量氮素存在下的降解和迁移规律，明晰其赋存特征；以拟南芥、非靶标有益植物大豆和非靶标有害植物蓝藻为模式生物，从生长影响、氧化损伤和藻毒素释放等方面，探讨过量氮素对除草剂生态毒性效应的手性选择性影响；利用同步辐射技术和碳、氮稳定同位素技术，结合常规分析技术深入解析手性除草剂迁移转化途径和植物氮代谢相关过程，揭示过量氮素对手性除草剂生态毒性对映体选择性影响的分子机制。预期成果将有助于对手性除草剂在富营养化背景下合理使用和环境安全提供更加准确、客观的预测与评价。

目前，我国粮食产量增加的两大驱动因子(化肥和农药)已显著影响环境质量而成为热点问题。因此，农药环境生态毒性效应研究中，除了关注污染物本身结构差异外，过量氮素的协同影响也不容忽视。主要研究结果如下：.（1）不同氮素水平下Rac-异丙甲草胺与S-异丙甲草胺对铜绿微囊藻细胞完整性及微囊藻毒素产生与释放影响差异研究。氮元素浓度越高，两种构型的异丙甲草胺对铜绿微囊藻的毒性越大。固定氮元素浓度，随着S-异丙甲草胺暴露浓度的增高，extra-MC-RR浓度逐渐增高，而intra-MC-RR浓度逐渐降低，总毒素浓度不断降低，胞外毒素所占总毒素的比例不断增高。在S-异丙甲草胺与Rac-异丙甲草胺增强铜绿微囊藻毒素外排的过程中，氮元素的贡献能力产生了明显的差异。.（2）S-异丙甲草胺对铜绿微囊藻的毒性大于Rac-异丙甲草胺，四个对映异构体对铜绿微囊藻的毒性大小依次是aRS> aSS> aSR>aRR。S-异丙甲草胺毒性明显大于其他四个异构体任何一个的毒性，我们推测aSS与aRS两异构具有协同作用。S-异丙甲草胺及其所包含的任何一个构型处理铜绿微囊藻细胞后，都会导致藻细胞内铁元素聚集。.（3） 在对映体的水平上比较了DCPP对拟南芥体内氮元素吸收和同化、氨基酸合成和氮稳定同位素分馏的影响。结果表明，(R)-DCPP明显抑制了拟南芥对NO3-的吸收，促进了NH4+的吸收，提高了硝酸还原酶的活性而抑制了亚硝酸还原酶的活性，(S)-DCPP的作用效果相对较小；在氮稳定同位素分馏方面，比较了不同氮源（NO3- 或NH4+）的影响，发现NH4+会使得拟南芥体内氮分馏的数值更加的负；进一步测定DCPP处理对拟南芥体内氮分馏的影响，发现具有除草活性的(R)-DCPP使得氮分馏的数值更负，而(S)-DCPP与对照组相类似，表明DCPP一定程度上是通过影响拟南芥对NH4+进行过量的选择性吸收，进而表现出毒性。.研究贴近真实环境氮元素浓度时手性除草剂的毒性效应有助于对手性除草剂在富营养化背景下合理使用和环境安全提供更加准确、客观的预测与评价。