Stomatal responses to leaf-to-air vapour pressure deficit in sahelian species

Stomatal response to leaf-to-air vapour pressure deficit (LAVPD) was studied in the annual arid zone C-4 grasses Schoenefeldia gracilis, Dactyloctenium aegyptium and Eragrostis tremula and in the C-3 Species, convolvulus, Ipomoea pes-tigridis and Ipomoea vagans. Stomatal responses to LAVPD were consistent with the drought survival strategies adopted by the different species. In draught resistant species (S. gracilis, I. vagans and I. pes-tigridis) stomatal conductance showed a negative response to increasing LAVPD whereas, in drought escaping species (D. aegyptium and E. tremula), stomatal conductance was independent of LAVPD. These observations suggest that resistance to drought was associated with stomatal closure as LAVPD increased, thus reducing the negative effect of a higher evaporative demand on water use efficiency, whereas in drought escaping species stomata showed no response to increasing evaporative demand in the atmosphere.