Figure 1. Midday foliage abscisic acid (ABA) level as leaf water potential (Ψl) declines during soil drought in angiosperm speciesUmbellularia californica (A) and conifer species Callitris rhomboidea (B). Mean leaf water potential (Ψl) at turgor loss point and standard errors are shown as grey solid and dashed lines vertical dashed grey line in A and B. Midday canopy conductance during soil drought in U. californica (C) and C. rhomboidea (D). Vertical dashed lines in C and D represent the Ψl at which peak foliage ABA level occurred. Generalized additive model (GAM) curves and standard errors are represented in all relationships by solid and dashed black lines, respectively.