冻融作用影响黑土毒死蜱农药降解的关键过程与机制

Freeze-thaw effect causes change of soil structure and organic carbon fraction, affecting progress of microbial degradation of pesticides. The research object is black soil, and chlorpyrifos is a kind of commonly used organophosphorus pesticide as goal pollutant. We simulate different freeze-thaw intensity, such as freeze temperatures, freeze-thaw cycles and soil water content, studying the response characteristic of soil active organic carbon fraction, aggregate stability, bulk density and pore to freeze-thaw intensity. The coupling relationship between active organic carbon fraction, soil structure and biotic community is studied to reveal mechanism of microbial degradation pesticide affecting by freeze-thaw intensity. Through technology of different aggregate crushed up and forming soil again, different active organic carbon fraction content affecting biotic community is studied to reveal the biotic mechanism of soil active organic carbon fraction controlling chlorpyrifos degradation. Through quantitative controlling technology of soil texture transformation, bulk density regulation and pumping pesticide into pores, soil aggregate stability, bulk density and pore affecting biotic community is studied. The study is revealed to the mechanism of microbial degradation chlorpyrifos regulated by abiotic factors influencing soil structure, such as soil texture, bulk density, and pore. This knowledge will provide a basis to further study the pesticide fate of agriculture soil in freeze-thaw period and to accelerate soil pesticide degradation caused by good agricultural practice.

冻融作用改变土壤结构和有机碳组分，制约微生物降解农药行为。本项目以黑土为研究对象，以常用有机磷农药毒死蜱为目标污染物，通过模拟实验控制冻结温度、冻融次数及土壤含水率等条件，研究土壤活性有机碳组分、团聚体稳定性、容重及孔隙对冻融强度的响应特征，明确活性有机碳组分、土壤结构与微生物群落的耦合关系，揭示冻融强度影响微生物降解农药的机理；通过不同粒级团聚体压碎重塑土壤技术，研究初始土壤活性有机碳组分不同对微生物群落的影响，揭示土壤活性有机碳组分控制毒死蜱降解的生物学机制；通过土壤质地改造、容重调节以及农药进入孔隙等定量控制技术，研究初始土壤团聚体稳定性、容重及孔隙变化对微生物群落的影响，揭示质地、容重及孔隙等决定土壤结构的各非生物因素反馈调控微生物降解毒死蜱机制。理论上将为深入研究冻融期农田土壤农药归趋行为奠定基础，实践上将为通过优化农田管理措施来加快土壤农药降解提供依据。

冻融作用会改变土壤结构和有机碳组分，制约微生物降解农药行为。本项目以黑土为研究对象，以毒死蜱为目标污染物，通过模拟实验控制冻结温度（-15℃、-5℃）、冻融次数、土壤含水率（田间最大持水量MWHC30%、60%、90%）及初始毒死蜱含量（10、20、50mg kg-1）等条件，研究表明：在30次的冻融频次内，毒死蜱半衰期约为46.2d ~ 138.6d，降解速率常数约为0.005d-1 ~ 0.015d-1；降解过程符合一级动力学方程，初始毒死蜱含量越高，降解速率越低，半衰期越长；与CK5（对照培养温度5℃）相比，FTC-5-5（冻结温度-5℃，解冻温度5℃）比FTC-15-5（冻结温度-15℃，解冻温度5℃）条件下黑土毒死蜱降解速率快；冻融作用下黑土60% MWHC毒死蜱降解速率最快，30% MWHC降解速率其次，但过高的黑土初始含水率90% MWHC不利于毒死蜱降解。不同的冻融强度对黑土基本理化性质影响不同，随着冻融频次增加，黑土EC、pH值表现为先降低后增加趋势，DOC表现为先降低后增加再减少趋势，团聚体平均重量直径（MWD）表现为逐渐降低趋势，MBC表现为先增加后减少趋势，土壤含水率越高，冻结温度越高，MBC含量越小；与CK5相比，冻融作用能降低黑土细菌、真菌、放线菌PLFA含量，但黑土中微生物经历冻融循环后，适应了低温环境，与冻融初期相比，PLFA含量有增加趋势。冻融作用下0.25-1mm粒径毒死蜱降解速率最高，1-2mm粒径其次，<0.25mm粒径降解速率最小。通过添加黏土矿物改造质地，保证初始微生物群落相同条件下，冻融作用下添加10%粉砂及黏粒级（<0.053 mm）毒死蜱降解速率最大，10%细砂级（0.25-0.053 mm）其次，对照组无添加降解速率最小。通过模拟机械压实改变土壤容重，黑土容重越大，毒死蜱降解速率越小。通过外源添加葡萄糖改变土壤中微生物的营养状况，保证初始微生物群落相同条件下，葡萄糖1%初始添加量使黑土毒死蜱降解速率最快。本研究表明冻融期土壤微生物保持活性，仍能降解农药，但受多种因素制约，本项目为深入研究冻融期农田土壤农药归趋行为奠定基础，实践上为通过优化农田管理措施来加快土壤农药降解提供依据。