Forest Dynamics. Swiss Federal Research Institute WSL, Birmensdorf, Switzerland.
PLoS One. 2013 Jul 22;8(7):e69171. doi: 10.1371/journal.pone.0069171. Print 2013.
Despite abatement programs of precursors implemented in many industrialized countries, ozone remains the principal air pollutant throughout the northern hemisphere with background concentrations increasing as a consequence of economic development in former or still emerging countries and present climate change. Some of the highest ozone concentrations are measured in regions with a Mediterranean climate but the effect on the natural vegetation is alleviated by low stomatal uptake and frequent leaf xeromorphy in response to summer drought episodes characteristic of this climate. However, there is a lack of understanding of the respective role of the foliage physiology and leaf xeromorphy on the mechanistic effects of ozone in Mediterranean species. Particularly, evidence about morphological and structural changes in evergreens in response to ozone stress is missing.
Our study was started after observing ozone -like injury in foliage of holm oak during the assessment of air pollution mitigation by urban trees throughout the Madrid conurbation. Our objectives were to confirm the diagnosis, investigate the extent of symptoms and analyze the ecological factors contributing to ozone injury, particularly, the site water supply. Symptoms consisted of adaxial and intercostal stippling increasing with leaf age. Underlying stippling, cells in the upper mesophyll showed HR-like reactions typical of ozone stress. The surrounding cells showed further oxidative stress markers. These morphological and micromorphological markers of ozone stress were similar to those recorded in deciduous broadleaved species. However, stippling became obvious already at an AOT40 of 21 ppm•h and was primarily found at irrigated sites. Subsequent analyses showed that irrigated trees had their stomatal conductance increased and leaf life -span reduced whereas the leaf xeromorphy remained unchanged. These findings suggest a central role of water availability versus leaf xeromorphy for ozone symptom expression by cell injury in holm oak.
尽管许多工业化国家都实施了前体物质减排计划，但臭氧仍然是北半球主要的空气污染物，由于前工业化国家或新兴国家的经济发展以及当前的气候变化，背景浓度不断增加。在具有地中海气候的地区，臭氧浓度最高，但由于这种气候夏季干旱频繁，导致气孔吸收减少和叶片常出现旱生结构，从而减轻了对自然植被的影响。然而，对于臭氧在地中海物种中的机制作用，叶片生理学和叶片旱生性的各自作用，人们的理解还很缺乏。特别是，关于常绿植物对臭氧胁迫的形态和结构变化的证据还很缺乏。
在评估马德里城市群中城市树木对空气污染的缓解作用时，我们观察到了欧洲栓皮栎叶片中类似于臭氧的损伤，由此启动了我们的研究。我们的目标是确认诊断，调查症状的严重程度，并分析导致臭氧损伤的生态因素，特别是现场供水。症状表现为随着叶片年龄的增加，叶片的正面和肋骨上出现点状斑纹。底层的斑纹处，上表皮层的细胞显示出典型的臭氧胁迫的 HR 样反应。周围的细胞显示出进一步的氧化应激标志物。这些臭氧胁迫的形态和微观形态标记与在落叶阔叶树种中记录的标记相似。然而，在 AOT40 为 21 ppm•h 时，点状斑纹已经很明显，主要出现在灌溉的地点。随后的分析表明，灌溉树木的气孔导度增加，叶片寿命缩短，而叶片旱生性保持不变。这些发现表明，在欧洲栓皮栎中，水的可利用性相对于叶片旱生性在细胞损伤导致臭氧症状表达方面起着核心作用。
