Despite representing a sizeable fraction of the canopy, very little is known about leaf sheath gas exchange in grasses. Specifically, estimates of sheath stomatal conductance, transpiration and photosynthesis along with their responses to light, CO₂ and vapour pressure deficit (VPD) are unknown. Furthermore, the anatomical basis of these responses is poorly documented. Here, using barley as a model system, and combining leaf‐level gas exchange, whole‐plant gravimetric measurements, transpiration inhibitors, anatomical observations, and biophysical modelling, we found that sheath and blade stomatal conductance and transpiration were similar, especially at low light, in addition to being genotypically variable. Thanks to high abaxial stomata densities and surface areas nearly half those of the blades, sheaths accounted for up to 17% of the daily whole‐plant water use, which ‐surprisingly‐ increased to 45% during the nighttime. Sheath photosynthesis was on average 17–25% that of the blade and was associated with lower water use efficiency. Finally, sheaths responded differently to the environment, exhibiting a lack of response to CO₂ but a strong sensitivity to VPD. Overall, these results suggest a key involvement of sheaths in feedback loops between canopy architecture and gas exchange with potentially significant implications on adaptation to current and future climates in grasses.

中文翻译：

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护套叶片：护套对草料作物中白天和夜间气体交换的重要贡献。

尽管占冠层很大一部分，但对草中的叶鞘气体交换知之甚少。具体而言，估计鞘气孔导度，蒸腾作用和光合作用及其对光，CO ₂的响应和蒸气压不足（VPD）未知。此外，这些反应的解剖学基础文献很少。在这里，以大麦为模型系统，并结合叶级气体交换，全植物重量测量，蒸腾抑制剂，解剖观察和生物物理模型，我们发现鞘和叶片气孔电导率和蒸腾作用相似，尤其是在弱光下，除了具有基因型上的可变性。由于高的背面气孔密度和近一半的叶片表面积，鞘管占全厂日常用水的17％，令人惊讶的是，在夜间，鞘管的用水量增加到45％。鞘的光合作用平均为叶片的17–25％，并且与较低的水分利用效率有关。最后，₂但对VPD的敏感度很高。总的来说，这些结果表明鞘管在冠层结构和气体交换之间的反馈回路中的关键作用，对适应当前和未来的草木气候具有潜在的重大影响。