Whole-plant hydraulic integration is linked to multiscale anatomical coordination in evergreen broad-leaved trees

Whole-plant hydraulic strategies depend on coordinated hydraulic structure and function across organs. However, how hydraulic safety, efficiency and water storage are integrated across the whole plant and linked to multiscale xylem anatomy remains poorly understood. We quantified hydraulic traits in leaves, stems, and coarse roots of 12 dominant tree species from a northern tropical evergreen broad-leaved forest. We also characterised their xylem anatomy at pit, vessel and tissue scales. Coarse roots were more vulnerable to embolism than stems and leaves, but had higher theoretical hydraulic conductivity (Kth) and hydraulic capacitance (C). Leaves had the lowest Kth and C and the most negative turgor loss point. Stems had water potentials at 50% embolism formation (P50) comparable to those of leaves, whereas their C values were intermediate between leaves and coarse roots. Principal component analysis separated species along aboveground and belowground hydraulic axes, with the aboveground axis associated mainly with embolism resistance and water potential buffering, and the belowground axis associated with water acquisition and storage. Across organs, covariation between P50 and C suggested a trade-off between embolism resistance and water-storage capacity, consistent with contrasting drought-tolerance and drought-avoidance hydraulic strategies. Intervessel pit membrane surface area was associated with Kth and C, vessel grouping traits with P50, and tissue allocation indirectly with P50 through C. Together, these findings suggest that whole-plant hydraulic strategies in evergreen broad-leaved trees reflect organ specialisation and multiscale anatomical coordination rather than variation along a single dominant hydraulic axis.