Aquaporin regulation in roots controls plant hydraulic conductance, stomatal conductance, and leaf water potential in Pinus radiata under water stress

Stomatal regulation is crucial for forest species performance and survival on drought-prone sites. We investigated the regulation of root and shoot hydraulics in three Pinus radiata clones exposed to drought stress and its coordination with stomatal conductance (g(s)) and leaf water potential (psi(leaf)). All clones experienced a substantial decrease in root-specific root hydraulic conductance (Kroot-r) in response to the water stress, but leaf-specific shoot hydraulic conductance (Kshoot-l) did not change in any of the clones. The reduction in Kroot-r caused a decrease in leaf-specific whole-plant hydraulic conductance (Kplant-l). Among clones, the larger the decrease in Kplant-l, the more stomata closed in response to drought. Rewatering resulted in a quick recovery of Kroot-r and g(s). Our results demonstrated that the reduction in Kplant-l, attributed to a down regulation of aquaporin activity in roots, was linked to the isohydric stomatal behaviour, resulting in a nearly constant psi(leaf) as water stress started. We concluded that higher Kplant-l is associated with water stress resistance by sustaining a less negative psi(leaf) and delaying stomatal closure.