Centro Internactional De Agricultura Tropical, A.A. 6713, CALI, Colombia.
Photosynth Res. 1985 Jan;7(2):137-49. doi: 10.1007/BF00037004.
The gas exchange of 19 widely different warm climate species was observed at different leaf to air vapour pressure deficits (VPD). In all species stomata tended to close as VPD increased resulting in a decrease in net photosynthesis. The absolute reduction in leaf conductance per unit increase in VPD was greatest in those species which had a large leaf conductance at low VPDs. This would be expected even if stomata of all species were equally sensitive. However the percentage reduction in net photosynthesis (used as a measure of the relative sensitivity of stomata of the different species) was also closely related to the maximal conductance at low VPD. Similarily the relative sensitivity of stomata to changes in VPD was closely related to the weighted stomatal density or 'crowding index'.The hypothesis is presented that stomatal closure at different VPDs is related to peristomatal evaporation coupled with a high resistance between the epidermis and the mesophyll and low resistance between the stomatal apparatus and the epidermal cells. This hypothesis is consistent with the greater relative sensitivity of stomata on leaves with a high crowding index.The results and the hypothesis are discussed in the light of selection, for optimal productivity under differing conditions of relative humidity and soil water availablility, by observation of stomatal density and distribution on the two sides of the leaf.
观察了 19 种广泛不同的暖气候物种在不同叶片与空气蒸汽压差（VPD）下的气体交换。在所有物种中，气孔随着 VPD 的增加而趋于关闭，导致净光合作用减少。在 VPD 升高时，每单位 VPD 增加导致叶片导度绝对减少最大的那些物种，其在低 VPD 时有较大的叶片导度。即使所有物种的气孔都同样敏感，也可以预期到这一点。然而，净光合作用的减少百分比（用作不同物种气孔相对敏感性的衡量标准）也与低 VPD 下的最大导度密切相关。类似地，气孔对 VPD 变化的相对敏感性与加权气孔密度或“拥挤指数”密切相关。提出了一个假说，即不同 VPD 下的气孔关闭与周缘蒸发有关，同时表皮和叶肉之间的阻力较高，而气孔装置和表皮细胞之间的阻力较低。这个假说与高拥挤指数叶片上气孔具有更高相对敏感性的观察结果一致。根据在不同的相对湿度和土壤水分可利用性条件下观察到的气孔密度和分布，对结果和假说进行了讨论，以选择最佳生产力。
