How does elevated tropospheric ozone exposure affect plant health over time?

由于工业和运输污染，对流层臭氧是通过NOx(NO和NO2)碳氢化合物和挥发性有机化合物(VOCs)1之间的自由基机制的光催化形成的。自1950年代以来，全球对流层臭氧污染有所增加，2尽管欧洲和北美的臭氧前体排放量自1990年代以来一直停滞不前，但亚洲和南美洲产生的臭氧污染的长距离输送继续提高欧洲的基线3。臭氧暴露对人类和植物的健康都构成重大风险5，并具有辐射强迫效应。6.臭氧暴露会导致植物体内的氧化应激，导致植物释放更多的挥发性有机化合物，进而通过正反馈效应增加臭氧的产生8。臭氧对植被的其他关键影响是早期落叶(落叶)和生长减少。臭氧暴露影响了关键的生长阶段，增加了对干旱的敏感性，并减少了氮素对根生物量积累的积极影响。在生态系统一级，臭氧暴露通过关闭气孔来限制蒸腾作用，从而降低初级生产力。臭氧对森林的损害可以通过树冠脱落、变色和树叶伤害来远程监测。联合英国陆地环境模拟器(JLES)是作为英国气象局和NERC地球系统模拟战略的一部分开发的陆地表面模型。Jules目前使用气孔导度对生长的影响作为与臭氧有关的单一参数(臭氧暴露降低了导度)，然而臭氧污染对植被的影响是复杂的11。人们对慢性臭氧暴露与急性臭氧暴露的影响知之甚少。此外，树木对不断变化的臭氧暴露的长期反应仍然存在疑问。例如，就生长而言，树木在多大程度上适应不断上升的臭氧基线？关于臭氧暴露是否限制了植物的二氧化碳吸收，或者在二氧化碳增加的情况下减少的气孔通量是否保护植被免受臭氧暴露的影响，还存在争议。更好地理解臭氧暴露的变化如何影响生态系统中的植被，将使地球系统模型(如Jules)能够更好地描述植物如何在时间和空间尺度上响应臭氧通量。这种对近地表臭氧污染的改进表示将使地球系统模型能够更好地预测气候变化中未来的碳平衡。通过卫星数据分析，臭氧暴露对全球植被健康的影响有哪些？臭氧暴露如何转化为树木的生理变化？树木是否适应了长期的臭氧暴露？长期不断变化的臭氧暴露如何影响树木的生长模式？如何改进地球系统模型中的植被对臭氧的反应，以包括更长期的生长反应，以及可能与过去的接触有关的对臭氧暴露的敏感性的差异？

Tropospheric ozone forms via photocatalysis of a free radical mechanism between NOx (NO and NO2) hydrocarbons and Volatile Organic Compounds (VOCs)1, resulting from industrial and transport pollution. Tropospheric ozone pollution has increased globally since 1950s2, and although ozone precursor emissions have plateaued in Europe and North America since the 1990s, long-range transport of ozone pollution produced in Asia and South America continues to raise European baselines3. Ozone exposure poses a major risk to both human4 and plant health5, as well as having a radiative forcing effect6.Ozone exposure causes oxidative stress in vegetation, leading to the increased release of VOCs by plants7 which in turn increase ozone production via a positive feedback effect8. Other key impacts of ozone on vegetation are early leaf drop (defoliation) and reduced growth. Ozone exposure affects critical growth stages, increases drought sensitivity and reduces the positive impact of nitrogen on root biomass accumulation9. At an ecosystem level, ozone exposure decreases primary productivity by limiting transpiration10 via stomatal closure. Ozone damage in forests can be monitored remotely via crown defoliation, discoloration and foliar injury.The Joint UK Land Environment Simulator (JULES) is a land surface model developed as a component of the Met Office and NERC Earth System Modelling Strategy. JULES currently uses the impact of stomatal conductance on growth as the single ozone linked parameter (ozone exposure reduces conductance), however the effects of ozone pollution on vegetation are complex11. The impact of chronic versus acute ozone exposure is poorly understood. Additionally, questions remain about long-term tree responses to changing ozone exposure. For example, to what degree do trees adapt to rising ozone baselines in terms of growth? There is debate as to whether ozone exposure limits plant CO2 uptake, or whether decreased stomatal flux under enhanced CO2 protects vegetation from ozone exposure.A better understanding of how changing ozone exposure affects vegetation in ecosystems would allow Earth system models, such as JULES, to better represent how plants respond to ozone fluxes across temporal and spatial scales. This improved representation of near surface ozone pollution would allow Earth system models to better predicts future carbon balances in a changing climate12.Chapter questions:1). What changes in global vegetation health can be attributed to ozone exposure via satellite data analysis?2). How does ozone exposure translate to physiological changes in trees? Do trees acclimate to chronic ozone exposure?3). How has changing ozone exposure over long time scales affected growth patterns in trees?4). How can the vegetation response to ozone in Earth System Models be improved to include longer term growth responses, as well as differences in susceptibility to ozone exposure potentially linked to past exposure?