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Leaf hydraulic traits are considered the key determinants of gas exchange and therefore affect species distributions along environmental gradients, but the patterns of leaf hydraulic traits and their associations with gas exchange across altitudinal gradients remain largely unknown.Here, we measured leaf hydraulic traits, gas exchange, leaf anatomical traits and plant size traits in two dominant alpine shrubs (Caragana jubata and Salix gilashanica) across an altitudinal gradient from 3100 to 3700 m.The findings indicated that with increasing altitude, both shrub species exhibited an increase in leaf hydraulic safety (more negative KleafP50), a decrease in leaf hydraulic efficiency (Kleaf‐max) and an increase in intrinsic water use efficiency (WUEi), thus allowing them to adapt to higher altitude habitats. The more negative KleafP50 was associated with a greater ratio of major to minor vein density (VLAmaj/VLAmin), the lower Kleaf‐max was associated with a lower minor vein density (VLAmin) and greater increase in WUEi arose from the small decrease in the photosynthetic rate relative to the stomatal conductance. However, C. jubata was consistent with the 'hydraulic safety strategy' with a great decrease in KleafP50, a small decrease in Kleaf‐max and a small increase in WUEi along with decreasing plant height and leaf area with increasing altitude. Whereas S. gilashanica was consistent with the 'photosynthetic efficiency strategy' with a small decrease in KleafP50, a greater decrease in Kleaf‐max and a greater increase in WUEi along with an increasing plant height and unchanged leaf area with increasing altitude.Overall, these findings provide new insights to improve understanding how shift in leaf hydraulic traits and their associations with gas exchange and plant size allow plants to adapt to high‐altitude habitats. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

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 (Ψ stem), maximum stem hydraulic conductivity (K stem-max), water potential at 50% loss of hydraulic conductivity (K stem   P 50) and anatomical traits of Caragana korshinkii resprouts were measured during a 1- to 13-year post-disturbance period. We found that the K stem-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 (F ap) and the sum of aperture area on per unit intervessel wall area (A ap). The K stem   P 50 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 F ap and A ap. 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. [ABSTRACT FROM AUTHOR]

Summary: Clarifying the coordination of leaf hydraulic traits with gas exchange across closely‐related species adapted to varying rainfall can provide insights into plant habitat distribution and drought adaptation.The leaf hydraulic conductance (Kleaf), stomatal conductance (gs), net assimilation (A), vein embolism and abscisic acid (ABA) concentration during dehydration were quantified, as well as pressure–volume curve traits and vein anatomy in 10 Caragana species adapted to a range of mean annual precipitation (MAP) conditions and growing in a common garden.We found a positive correlation between Ψleaf at 50% loss of Kleaf (KleafP50) and maximum Kleaf (Kleaf‐max) across species. Species from low‐MAP environments exhibited more negative KleafP50 and turgor loss point, and higher Kleaf‐max and leaf‐specific capacity at full turgor, along with higher vein density and midrib xylem per leaf area, and a higher ratio of Kleaf‐max : maximum gs. Tighter stomatal control mediated by higher ABA accumulation during dehydration in these species resulted in an increase in hydraulic safety and intrinsic water use efficiency (WUEi) during drought.Our results suggest that high hydraulic safety and efficiency combined with greater stomatal sensitivity triggered by ABA production and leading to greater WUEi provides drought tolerance in Caragana species adapted to low‐MAP environments. [ABSTRACT FROM AUTHOR]