Stomatal Behaviour of Kenaf and Sorghum in a Semiarid Tropical Environment. II. During the Day

Abstract

The influence of leaf water potential (Ψ_l), saturation deficit (δe), and temperature on stornatal conductance (g_s) of kenaf and sorghum was determined at non-limiting quantum fluxes both at high and low soil water status in the field, and under controlled environment conditions. Sorghum stomata closed in response to Ψ_l in a manner consistent with the classical feedback control, while kenaf stomata responded directly to δe, independently of Ψ_l. The rate of decrease of g_s of kenaf with increasing δe was greater at higher temperatures. Also the stomata of stressed kenaf were less sensitive to δe than those of the well-watered crop due to the limitation in degree of stomatal opening imposed by water stress.

The degree of stomatal adjustment in kenaf was also assessed. In the stressed kenaf, the Ψ_l at half the maximum g_s was c. 0.17 MPa lower and g_s was more sensitive to decreases in Ψ_l, than in the well watered control. However, there was little difference in the Ψ_l at 95% stomatal closure.