Quantifying Sources of Atmospheric Methyl Halides

P.I.将通过量化甲基溴、甲基碘化物和甲基氯的生化相关来源，调查农业对大气中甲基卤化物排放的潜在影响。将在温室中对多种水稻品种和其他作物进行对照试验，以评估影响甲基卤化物排放率的因素，如温度、光照水平和植物发育状态。一个假设的酶驱动生产甲基卤化物的过程将通过测定叶盘样品中的酶活性来研究，同时测量排放物，以及使用咖啡酸进行酶抑制实验。实验将覆盖水稻的生长季节，以确定排放物是否集中在植物发育的任何阶段，以及排放物是否与甲烷的排放物相关。类似的实验将研究其他农作物（小麦、大麦、西兰花、油菜籽）。外生菌根真菌（EF）也是新发现的甲基溴和碘化物的来源；相关真菌被认为是氯甲烷的重要排放者。这些真菌的环境发生足以表明对全球大气的潜在意义。该项目将在实验室研究中调查EF物种的排放情况，并研究对这些排放的环境控制。该项目还将基于对这些栖息地甲基卤化物排放的新观测，测量盐沼和红树林的排放。斯坦福大学和宾夕法尼亚大学的研究人员将在该项目中展开合作。该项目的结果可作为大气光化学/输送模式的输入，以评估对区域对流层臭氧量的影响。排放数据应使我们大大提高对氯甲烷和甲基溴的自然和人为来源的相对作用的理解，并使我们对碘化甲酯的陆地来源有新的认识。

The P.I. will investigate the potential impacts of agriculture on methyl halide emissions to the atmosphere by quantifying biochemically related sources of methyl bromide, methyl iodide, and methyl chloride. Controlled experiments will take place on a variety of rice cultivars and other crops in a greenhouse to evaluate the factors that influence methyl halide emission rates, such as temperature, light level, and plant-development state. A hypothesized enzyme-driven process of production of methyl halides will be investigated by assaying enzyme activity in leaf-disk samples as emissions are measured, along with enzyme-inhibition experiments using caffeic acid. Experiments will cover the growing season of rice to determine if emissions are concentrated during any plant-development stage and if emissions correlate with those of methane. Similar experiments will study other crop plants (wheat, barley, broccoli, rapeseed). Ectomycorrhizal fungi (EF) are also newly identified sources of methyl bromide and iodide; related fungi have been known as significant emitters of methyl chloride. The environmental occurrence of these fungi is great enough to indicate potential significance for the global atmosphere. This project will survey emissions from EF species in lab studies and will study environmental controls on these emissions. The project will also measure emissions from salt marshes and mangroves, building on new observations of methyl halide emissions from these habitats. Researchers from Stanford University and the University of Pennsylvania will collaborate in the project. The results of the project will be useful as input to atmospheric photochemical/transport models to assess impact on regional tropospheric ozone amounts. The emissions data should lead to significant improvement in our understanding of the relative roles of natural and anthropogenic sources of methyl chloride and methyl bromide, and also to new views of terrestrial sources of methyl iodide.