Figure 5. Foliage abscisic acid (ABA) levels as leaf water potential
(Ψl) declines during soil drought in leaves taken from
girdled branches in the angiosperm species Umbellularia
californica (A) and conifer species Callitris rhomboidea (B).
Generalized additive model (GAM) curves and standard errors are
represented by solid and dashed black lines, respectively, for the ABA
data from girdled branches, and in grey from ABA data taken from intact
branches. The black vertical line depicts the Ψl at peak
foliage ABA level in girdled branches, and the grey vertical line the
Ψl at peak foliage ABA level in intact branches.