Canaval Eva, Millet Dylan B, Zimmer Ina, Nosenko Tetyana, Georgii Elisabeth, Partoll Eva Maria, Fischer Lukas, Alwe Hariprasad D, Kulmala Markku, Karl Thomas, Schnitzler Jörg-Peter, Hansel Armin
Department of Ion Physics and Applied Physics, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria.
Department of Soil, Water and Climate, University of Minnesota, 439 Borlaug Hall, St. Paul, MN, USA.
Commun Earth Environ. 2020;1:44. doi: 10.1038/s43247-020-00041-2. Epub 2020 Nov 4.
Isoprene is emitted from the biosphere into the atmosphere, and may strengthen the defense mechanisms of plants against oxidative and thermal stress. Once in the atmosphere, isoprene is rapidly oxidized, either to isoprene-hydroxy-hydroperoxides (ISOPOOH) at low levels of nitrogen oxides, or to methyl vinyl ketone (MVK) and methacrolein at high levels. Here we combine uptake rates and deposition velocities that we obtained in laboratory experiments with observations in natural forests to show that 1,2-ISOPOOH deposits rapidly into poplar leaves. There, it is converted first to cytotoxic MVK and then most probably through alkenal/ one oxidoreductase (AOR) to less toxic methyl ethyl ketone (MEK). This detoxification process is potentially significant globally because AOR enzymes are ubiquitous in terrestrial plants. Our simulations with a global chemistry-transport model suggest that around 6.5 Tg yr of MEK are re-emitted to the atmosphere. This is the single largest MEK source presently known, and recycles 1.5% of the original isoprene flux. Eddy covariance flux measurements of isoprene and MEK over different forest ecosystems confirm that MEK emissions can reach 1-2% those of isoprene. We suggest that detoxification processes in plants are one of the most important sources of oxidized volatile organic compounds in the atmosphere.
异戊二烯从生物圈排放到大气中，可能会增强植物抵御氧化应激和热应激的防御机制。一旦进入大气，异戊二烯会迅速氧化，在低氮氧化物水平下氧化为异戊二烯 - 羟基 - 氢过氧化物（ISOPOOH），在高氮氧化物水平下氧化为甲基乙烯基酮（MVK）和甲基丙烯醛。在这里，我们将在实验室实验中获得的吸收速率和沉积速度与天然森林中的观测结果相结合，以表明1,2 - ISOPOOH会迅速沉积到杨树叶片中。在那里，它首先转化为具有细胞毒性的MVK，然后很可能通过烯醛/单氧化还原酶（AOR）转化为毒性较小的甲基乙基酮（MEK）。这种解毒过程在全球范围内可能具有重要意义，因为AOR酶在陆生植物中普遍存在。我们使用全球化学传输模型进行的模拟表明，每年约有6.5 Tg的MEK重新排放到大气中。这是目前已知的最大的单一MEK来源，并且回收了原始异戊二烯通量的1.5%。对不同森林生态系统中异戊二烯和MEK的涡度协方差通量测量证实，MEK排放量可达到异戊二烯排放量的1 - 2%。我们认为植物中的解毒过程是大气中氧化挥发性有机化合物的最重要来源之一。
