Abstract: A steady-state model of stomatal regulation has been developed, which includes a water flow system involving the effect of root-originated ABA. The influences of vapour pressure deficiency (VPD), air temperature and water content in the uppermost soil layer ( θs1 ) on leaf water potential, ABA concentration in xylem sap ([ ABA]x) and stomatal conductance had been simulated. The resuits show that changes in VPD and air temperature affect the leaf water potential and stomatal conductance, in which the [ABA]x played a decisive role in controlling the extent of their affect, although they had very littly effect on [ ABA] x itself.

Key words: Simulation, Vapour pressure deficiency, Air temperature, Soil water content, ABA, Stomatal conductance