Hydraulic traits are coordinated with maximum plant height at the global scale

Water must be transported long distances in tall plants, resulting in increasing hydraulic resistance, which may place limitations on the maximum plant height (H-max) in a given habitat. However, the coordination of hydraulic traits with H(max)( )and habitat aridity remains poorly understood. To explore whether H-max modifies the trade-off between hydraulic efficiency and safety or how water availability might influence the relationship between H-max and other hydraulic traits, we compiled a dataset including H-max and 11 hydraulic traits for 1281 woody species from 369 sites worldwide. We found that taller species from wet habitats exhibited greater xylem efficiency and lower hydraulic safety, wider conduits, lower conduit density, and lower sapwood density, which were all associated with habitat water availability. Plant height and hydraulic functioning appear to represent a single, coordinated axis of variation, aligned primarily with water availability, thus suggesting an important role for this axis in species sorting processes.