A clear trade-off between leaf hydraulic efficiency and safety in an aridland shrub during regrowth

It has been suggested that a trade-off between hydraulic efficiency and safety is related to drought adaptation across species. However, whether leaf hydraulic efficiency is sacrificed for safety during woody resprout regrowth after crown removal is not well understood. We measured leaf water potential (ψ_leaf) at predawn (ψ_pd) and midday (ψ_mid), leaf maximum hydraulic conductance (K_leaf-max), ψ_leaf at induction 50% loss of K_leaf-max (K_leaf P₅₀), leaf area-specific whole-plant hydraulic conductance (LSC), leaf vein structure and turgor loss point (π_tlp) in 1- to 13-year-old resprouts of the aridland shrub (Caragana korshinskii). ψ_pd was similar, ψ_mid and K_leaf P₅₀ became more negative, and K_leaf–max decreased in resprouts with the increasing age; thus, leaf hydraulic efficiency clearly traded off against safety. The difference between ψ_mid and K_leaf P₅₀, leaf hydraulic safety margin, increased gradually with increasing resprout age. More negative ψ_mid and K_leaf P₅₀ were closely related to decreasing LSC and more negative π_tlp, respectively, and the decreasing K_leaf-max arose from the lower minor vein density and the narrower midrib xylem vessels. Our results showed that a clear trade-off between leaf hydraulic efficiency and safety helps C. korshinskii resprouts adapt to increasing water stress as they approach final size.