Abstract：
Plant leaf temperatures can differ from ambient air temperatures. A temperature gradient in a gas mixture gives rise to a phenomenon known as thermodiffusion, which operates in addition to ordinary diffusion. Whilst transpiration is generally understood to be driven solely by the ordinary diffusion of water vapour along a concentration gradient, we consider the implications of thermodiffusion for transpiration. We develop a new modelling framework that introduces the effects of thermodiffusion on the transpiration rate, E. By applying this framework, we quantify the proportion of E attributable to thermodiffusion for a set of physiological and environmental conditions, varied over a wide range. Thermodiffusion is found to be most significant (in some cases > 30% of E) when a leaf-to-air temperature difference coincides with a relatively small water vapour concentration difference across the boundary layer; a boundary layer conductance that is large as compared to the stomatal conductance; or a relatively low transpiration rate. Thermodiffusion also alters the conditions required for the onset of reverse transpiration, and the rate at which this water vapour uptake occurs.
摘要：
植物叶片温度可以不同于环境空气温度。气体混合物中的温度梯度引起称为热扩散的现象，它除了普通扩散之外还起作用。虽然蒸腾通常被理解为仅由水蒸气沿浓度梯度的普通扩散驱动，我们考虑了热扩散对蒸腾作用的影响。我们开发了一个新的建模框架，介绍了热扩散对蒸腾速率的影响，E.通过应用这一框架，我们量化了一组生理和环境条件下归因于热扩散的E的比例，在很宽的范围内变化。当叶片与空气的温度差与边界层上相对较小的水蒸气浓度差重合时，发现热扩散是最重要的（在某些情况下>E的30％）；与气孔导度相比，边界层导度较大；或蒸腾速率相对较低。热扩散也改变了反向蒸腾开始所需的条件，以及这种水蒸气吸收的速率。
