Coordinated Variation of Whole‐Plant Hydraulic Anatomical Traits in Quercus variabilis Seedlings Reflects Provenance‐Specific Climate Adaptation

ABSTRACT Plant hydraulic performance relies on the coordinated functioning of stomatal, mesophyll, and xylem architecture. However, intraspecific evidence for such integration across climate gradients remains limited. We grew 1‐year‐old Quercus variabilis seedlings from 15 climatically contrasted provenances in a randomized common garden and quantified 19 anatomical traits across leaves, stems, and taproots. Provenance mean annual temperature, precipitation, and humidity jointly explained most of the observed variations. Seedlings from warmer, wetter origins developed (i) thinner palisade but thicker spongy mesophyll and overall leaves, (ii) smaller, denser stomata, and (iii) wider vessels with thicker walls, higher parenchyma fractions, and reduced fiber content. Root parenchyma covaried with stomatal density, and vessel traits were closely aligned with leaf anatomy, revealing a provenance‐scale network that enhances hydraulic conductance, water storage, and stomatal responsiveness while potentially mitigating embolism risk. Although hydraulic vulnerability and conductivity were not directly measured, the convergence of vessel enlargement and wall thickening suggests a functional balance between efficiency and safety. Our findings provide the first intraspecific evidence that Q. variabilis integrates structural adjustments across organs in response to climate, offering new insight into adaptive evolution and informing the selection of drought‐resilient provenances.