Divergent stem hydraulic strategies of Caragana korshinskii resprouts following a disturbance.

Resprouting plants are distributed in many vegetation communities worldwide. With increasing resprout age post-severe-disturbance, new stems grow rapidly at their early age, and decrease in their growth with gradually decreasing water status thereafter. However, there is little knowledge about how stem hydraulic strategies and anatomical traits vary post-disturbance. In this study, the stem water potential (Ψstem), maximum stem hydraulic conductivity (Kstem-max), water potential at 50% loss of hydraulic conductivity (Kstem  P50) and anatomical traits of Caragana korshinkii resprouts were measured during a 1- to 13-year post-disturbance period. We found that the Kstem-max decreased with resprout age from 1-year-old resprouts (84.2 mol m-1 s-1 MPa-1) to 13-year-old resprouts (54.2 mol m-1 s-1 MPa-1) as a result of decreases in the aperture fraction (Fap) and the sum of aperture area on per unit intervessel wall area (Aap). The Kstem  P50 of the resprouts decreased from 1-year-old resprouts (-1.8 MPa) to 13-year-old resprouts (-2.9 MPa) as a result of increases in vessel implosion resistance (t/b)2, wood density (WD), vessel grouping index (GI) and decreases in Fap and Aap. These shifts in hydraulic structure and function resulted in an age-based divergence in hydraulic strategies i.e., a change from an acquisitive strategy to a conservative strategy, with increasing resprout age post-disturbance.

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 (ψleaf ) at predawn (ψpd ) and midday (ψmid ), leaf maximum hydraulic conductance (Kleaf-max ), ψleaf at induction 50% loss of Kleaf-max (Kleaf P50 ), leaf area-specific whole-plant hydraulic conductance (LSC), leaf vein structure and turgor loss point (πtlp ) in 1- to 13-year-old resprouts of the aridland shrub (Caragana korshinskii). ψpd was similar, ψmid and Kleaf P50 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 ψmid and Kleaf P50 , leaf hydraulic safety margin, increased gradually with increasing resprout age. More negative ψmid and Kleaf P50 were closely related to decreasing LSC and more negative πtlp , 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.