Fig. 4

Hypothetical variation in SCP with water availability at various timescales. (A) On short timescales in piñon pine (solid line), increased water availability decreases SCP, possibly by shifting Ψ_ABA (blue arrows), the trigger point for ABA production. (B) On short timescales (solid red line) under decreased leaf water potentials (Ψ_leaf), ABA increases in ‘R type’ species, like piñon pine (left panel), while ABA briefly increases, peaks and then declines in ‘P type’ species like juniper (right panel). Under rehydration (dashed blue lines), a more negative Ψ_leaf is required to trigger the same amount of ABA production in ‘R type’ species while ABA remains at low values in ‘P type’ species. (C) Piñon pine is unable to adjust turgor loss point (Ψ_TLP) (left panel), however, Ψ_TLP increases with increasing water availability in juniper (right panel). (D) In both piñon pine and juniper, structural acclimation may occur on both short and long timescales, increasing SCP in both species (A, dashed line).