气孔下腔间的水汽扩散

WATER VAPOUR DIFFUSION IN THE SUBSTOMATAL CAVITY

本文把气孔及其下腔看作截面为椭圆形的柱形区域,提出一个水汽从气孔下腔内所有细胞表面扩散到气孔外端的三维扩散模型。根据 Fick 定律和质量守恒定律建立了支配该模型的水汽扩散方程。用有限差分法,借助于计算机求得水汽从气孔下腔的所有细胞表面扩散到气孔内端所遇到的阻力及其近似表达式。并从理论上对该阻力的倒数——导度随气孔面积而变化的方式做了分析和解释。通过将本模型求得的气孔下腔阻力计算公式与 Brown 等以及 Cooke 的公式比较,发现在气孔开度变化相当大的范围内用后面两公式计算的阻力偏大0.5—1倍左右。此外,计算结果还表明:在气孔下腔水散失总量中,腔内表皮细胞表面上的水散失量占86—96%,而保卫细胞表面上的水散失量又占后者的88—93%,副卫细胞表面上的水散失量仅7—12%。

In this paper stomatal pore and substomatal cavity are considered to be elliptie cylinders. A three-dimensional diffusion model is presented,which describes the diffusion of vapour from the surfaces of the cells surrounding the cavity to the cuter end of the pore.Equations describing vapour diffusion in the model are set up,based on Fick's law and the law of con- servation of mass,and are solved by using computer.Quantitative relation between the cavity resistance to water vapour diffusion and stomatal aperture is obtained and is given more general theoretical explanation.Comparing the formula obtained in this paper with those Of Brown and Escombe and of Cooke et al.,it is found that the cavity resistance calculated by the latter two formulas are 0.5—1 times higher in a large range of stomatal aperture values.Besides,it is shown by calculating that the rates of loss from guard cells and subsidiary cells account for 88— 93% and 7—12% respectively of that from epidermic cells,and the Ltter amounts to 86—96% of that from all the cells in the cavity in the large range of stomatal change.