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

对流层臭氧是由工业和运输污染产生的氮氧化物（NO和NO2）碳氢化合物和挥发性有机化合物（VOCs）1之间的自由基机制光催化形成的。自20世纪50年代以来，对流层臭氧污染在全球范围内有所增加，尽管自20世纪90年代以来，欧洲和北美的臭氧前体排放已趋于稳定，但亚洲和南美洲产生的臭氧污染的远距离输送继续提高欧洲的基线。臭氧暴露对人类和植物健康都构成重大威胁，并具有辐射强迫效应。臭氧暴露会引起植被的氧化应激，导致植物释放更多的挥发性有机化合物，从而通过正反馈效应增加臭氧的产生。臭氧对植被的其他关键影响是早期落叶（落叶）和生长减缓。臭氧暴露会影响关键生长阶段，增加干旱敏感性，并降低氮对根系生物量积累的积极影响。在生态系统水平上，臭氧暴露通过气孔关闭限制蒸腾而降低初级生产力。森林中的臭氧破坏可以通过树冠落叶、变色和叶面损伤进行远程监测。联合英国陆地环境模拟器（JULES）是一个陆地表面模型，作为气象局和NERC地球系统建模战略的一个组成部分而开发。JULES目前使用气孔导度对生长的影响作为单一的臭氧相关参数（臭氧暴露降低导度），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和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问题。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？臭氧暴露是否限制了植物对CO2的吸收，或者在CO2增强的情况下气孔通量的减少是否保护植被免受臭氧暴露的影响，目前存在争议。更好地了解不断变化的臭氧暴露如何影响生态系统中的植被，将使地球系统模型，如JULES，能够更好地代表植物如何对跨时间和空间尺度的臭氧通量作出反应。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未来气候变化中的碳平衡。章的问题:1)。通过卫星数据分析，全球植被健康的哪些变化可归因于臭氧暴露？臭氧暴露如何转化为树木的生理变化？树木能适应长期的臭氧暴露吗？在长时间尺度上改变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植被对臭氧的反应，使其包括较长期的生长反应，以及可能与过去接触有关的对臭氧暴露的易感性差异？

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?