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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 P 50 ), 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 P 50 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 P 50 , leaf hydraulic safety margin, increased gradually with increasing resprout age. More negative ψ mid and K leaf P 50 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., (© 2021 John Wiley & Sons Ltd.)

Drought is a cyclical phenomenon in natural environments. During dehydration, stomatal closure is mainly regulated by abscisic acid (ABA) dynamics that limit transpiration in seed plants, but following rehydration, the mechanism of gas exchange recovery is still not clear. In this study, leaf water potential (ψ leaf ), stomatal conductance (g s ), leaf hydraulic conductance (K leaf ), foliar ABA level, ethylene emission rate in response to dehydration and rehydration were investigated in four Caragana species with isohydric (Caragana spinosa and C. pruinosa) and anisohydric (C. intermedia and C. microphylla) traits. Two isohydric species with ABA-induced stomatal closure exhibited more sensitive g s and K leaf to decreasing ψ leaf than two anisohydric species which exhibited a switch from ABA to water potential-driven stomatal closure during dehydration. Following rehydration, the recovery of gas exchange was not associated with a decrease in ABA level but was strongly limited by the degradation of the ethylene emission rate in all species. Furthermore, two anisohydric species with low drought-induced ethylene production exhibited more rapid recovery in gas exchange upon rehydration. Our results indicated that ethylene is a key factor regulating the drought-recovery ability in terms of gas exchange, which may shape species adaptation to drought and potential species distribution., (© 2020 John Wiley & Sons Ltd.)