Vapour pressure deficit is a major driver of seasonal changes in transpiration, but photoperiod also modulates leaf responses. Climate warming might enhance transpiration by increasing atmospheric water demand and the length of the growing season, but photoperiod-sensitive species could show dampened responses. Here, we document that day length is a significant driver of the seasonal variation in stomatal conductance. We performed weekly gas exchange measurements across a common garden experiment with 12 oak species from contrasting geographical origins, and we observed that the influence of day length was of similar strength to that of vapour pressure deficit in driving the seasonal pattern. We then examined the generality of our findings by incorporating day-length regulation into well-known stomatal models. For both angiosperm and gymnosperm species, the models improved significantly when adding day-length dependences. Photoperiod control over stomatal conductance could play a large yet underexplored role on the plant and ecosystem water balances.

中文翻译：

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日长调节栎属物种气孔导度的季节性模式。

蒸气压不足是蒸腾季节变化的主要驱动力，但光周期也会调节叶片的响应。气候变暖可能通过增加大气中的需水量和生长季节的长度来增强蒸腾作用，但是对光周期敏感的物种可能显示出减弱的反应。在这里，我们记录到天长是气孔导度季节性变化的重要驱动因素。我们在一个普通的花园实验中使用来自相反地理起源的12种橡树种进行了每周的气体交换测量，并且我们观察到了日长的影响与驱动季节性模式的蒸气压亏缺具有相似的强度。然后，我们通过将日长调节纳入著名的气孔模型中，检查了研究结果的一般性。对于被子植物和裸子植物，当增加日间依赖时，模型都得到了显着改善。光周期对气孔导度的控制可能在植物和生态系统的水平衡中起着很大但尚未被充分开发的作用。