Figure 2. Foliage phaseic acid (PA) levels as leaf water potential
(Ψl) declines during soil drought in the angiosperm
species Umbellularia californica (A) and conifer speciesCallitris rhomboidea (B). Generalized additive model (GAM) curves
and standard errors are represented by solid and dashed lines,
respectively. The grey vertical line depicts the Ψl at
peak foliage ABA level.