Boundary layer, stomatal geometry and -spacing, in relation to drought tolerance in four Nicotiana tabacum L. cultivars

Although numerous studies, both phenomenological and mathematical, have related gaseous interchanges at the plant leaf surface and atmospheric interface specifically with regard to drought tolerance, the important role of trichomes and the boundary layer has not been recognized. In this investigation the focus was restricted to the role of the boundary layer along with stomatal geometry and -spacing in determining the diffusional resistance to CO2 and H2O in four Nicotiana tabacum L. cultivars of different, but known, drought tolerance. Resistances were expressed both in terms of resistance components on a unit leaf area basis and in terms of dimensionless quantities. The abaxial leaf surface had the highest trichome frequency, more so in the drought tolerant than in the drought sensitive cultivars, being 9.7% and 6.9% higher than on the adaxial surface for TL33 and CDL28, as opposed to being 21.2% and 26.8% higher for GS46 and Elsoma, respectively. The frequency of the long glandular trichomes of epiderm...