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 C4 grasses Schoenefeldia gracilis , Dactyloctenium aegyptium and Eragrostis tremula and in the C3 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 drought 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.