Mesophyll conductance (Gm ) is one of the most important factors determining photosynthesis. Tropospheric ozone (O3 ) is known to accelerate leaf senescence and causes a decline of photosynthetic activity in leaves. However, the effects of age-related variation of O3 on Gm have not been well investigated, and we, therefore, analysed leaf gas exchange data in a free-air O3 exposure experiment on Siebold's beech with two levels (ambient and elevated O3 : 28 and 62 nmol mol-1 as daylight average, respectively). In addition, we examined whether O3 -induced changes on leaf morphology (leaf mass per area, leaf density and leaf thickness) may affect CO2 diffusion inside leaves. We found that O3 damaged the photosynthetic biochemistry progressively during the growing season. The Gm was associated with a reduced photosynthesis in O3 -fumigated Siebold's beech in August. The O3 -induced reduction of Gm was negatively correlated with leaf density, which was increased by elevated O3 , suggesting that the reduction of Gm was accompanied by changes in the physical structure of mesophyll cells. On the other hand, in October, the O3 -induced decrease of Gm was diminished because Gm decreased due to leaf senescence regardless of O3 treatment. The reduction of photosynthesis in senescent leaves after O3 exposure was mainly due to a decrease of maximum carboxylation rate (Vcmax ) and/or maximum electron transport rate (Jmax ) rather than diffusive limitations to CO2 transport such as Gm . A leaf age×O3 interaction of photosynthetic response will be a key for modelling photosynthesis in O3 -polluted environments. This article is protected by copyright. All rights reserved.

中文翻译：

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叶龄和臭氧对西博尔德山毛榉叶肉电导的交互作用

叶肉电导 (Gm) 是决定光合作用的最重要因素之一。已知对流层臭氧 (O3) 会加速叶片衰老并导致叶片光合活性下降。然而，O3 的年龄相关变化对 Gm 的影响尚未得到很好的研究，因此，我们分析了 Siebold 山毛榉的自由空气 O3 暴露实验中的叶片气体交换数据，具有两个水平（环境和升高的 O3：28和 62 nmol mol-1 作为日光平均值，分别）。此外，我们检查了 O3 引起的叶片形态变化（单位面积的叶片质量、叶片密度和叶片厚度）是否会影响叶片内的 CO2 扩散。我们发现 O3 在生长季节逐渐破坏光合生物化学。Gm 与 8 月 O3 熏蒸的 Siebold 山毛榉的光合作用减少有关。O3 诱导的 Gm 减少与叶片密度呈负相关，叶片密度随 O3 升高而增加，表明 Gm 的减少伴随着叶肉细胞物理结构的变化。另一方面，在 10 月，O3 引起的 Gm 减少减弱，因为 Gm 由于叶片衰老而减少，而不管 O3 处理如何。O3 暴露后衰老叶片光合作用的减少主要是由于最大羧化速率 (Vcmax) 和/或最大电子传输速率 (Jmax) 的降低，而不是对 CO2 传输的扩散限制，例如 Gm。光合响应的叶龄×O3 相互作用将是在 O3 污染环境中模拟光合作用的关键。本文受版权保护。版权所有。