Both ozone (O3 ) and drought can limit carbon fixation by forest trees. To cope with drought stress, plants have isohydric or anisohydric water use strategies. Ozone enters plant tissues through stomata. Therefore, stomatal closure can be interpreted as avoidance to O3 stress. Here, we applied an optimization model of stomata involving water, CO2 , and O3 flux to test whether isohydric and anisohydric strategies may affect avoidance of O3 stress by stomatal closure in four Mediterranean tree species during drought. The data suggest that stomatal closure represents a response to avoid damage to the photosynthetic mechanisms under elevated O3 depending on plant water use strategy. Under high-O3 and well-watered conditions, isohydric species limited O3 fluxes by stomatal closure, whereas anisohydric species activated a tolerance response and did not actively close stomata. Under both O3 and drought stress, however, anisohydric species enhanced the capacity of avoidance by closing stomata to cope with the severe oxidative stress. In the late growing season, regardless of the water use strategy, the efficiency of O3 stress avoidance decreased with leaf ageing. As a result, carbon assimilation rate was decreased by O3 while stomata did not close enough to limit transpirational water losses.

中文翻译：

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用水策略通过地中海树木气孔关闭影响避免臭氧胁迫-建模分析。

臭氧（O3）和干旱都会限制林木固碳。为了应对干旱胁迫，植物采取了等量或等量水的使用策略。臭氧通过气孔进入植物组织。因此，气孔关闭可以解释为避免O3压力。在这里，我们应用了涉及水，CO2和O3通量的气孔优化模型，以测试等渗和等渗策略是否可能通过干旱期间四种地中海树木物种的气孔关闭来避免O3胁迫。数据表明，气孔关闭是一种避免在较高的O3下破坏光合作用机制的响应，具体取决于植物的用水策略。在高O3和水分充足的条件下，等渗物质通过气孔关闭限制了O3通量，异水物种激活了耐受性反应，并没有主动关闭气孔。然而，在O3和干旱胁迫下，通过关闭气孔来应对严重的氧化胁迫，异水物种增强了避免的能力。在生长后期，无论采取何种用水策略，随着叶片衰老，避免O3胁迫的效率都会降低。结果，O3降低了碳的同化率，而气孔的闭合度不足以限制蒸腾水的损失。