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 (psi(leaf)) at predawn (psi(pd)) and midday (psi(mid)), leaf maximum hydraulic conductance (Kleaf-max), psi(leaf) at induction 50% loss of Kleaf-max (K-leaf P-50), leaf area-specific whole-plant hydraulic conductance (LSC), leaf vein structure and turgor loss point (pi(tlp)) in 1- to 13-year-old resprouts of the aridland shrub (Caragana korshinskii). psi(pd) was similar, psi(mid) and K-leaf P-50 became more negative, and Kleaf-max decreased in resprouts with the increasing age; thus, leaf hydraulic efficiency clearly traded off against safety. The difference between psi(mid) and K-leaf P-50, leaf hydraulic safety margin, increased gradually with increasing resprout age. More negative psi(mid) and K-leaf P-50 were closely related to decreasing LSC and more negative pi(tlp), respectively, and the decreasing Kleaf-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.