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To assess hydraulic architecture and limitations to water transport across whole trees, we compared xylem anatomy, vulnerability to cavitation (Ψ₅₀) and specific hydraulic conductivity (K_s) of stems, shallow roots and deep roots (from caves to 20 m depth) for four species: Juniperus ashei, Bumelia lanuginosa, Quercus fusiformis and Quercus sinuata.

Mean, maximum and hydraulically weighted (D_h) conduit diameters and K_s were largest in deep roots, intermediate in shallow roots, and smallest in stems (P < 0.05 for each). Mean vessel diameters of deep roots were 2.1–4.2‐fold greater than in stems, and K_s was seven to 38 times larger in the deep roots.

Ψ₅₀ also increased from stems to roots with depth, as much as 24‐fold from stems to deep roots in B. lanuginosa. For all species together, Ψ₅₀ was positively correlated with both D_h and K_s, suggesting a potential trade‐off exists between conducting …