Stomatal regulation, leaf water relations, and leaf phenology are coordinated in tree species from the Sonoran Desert

To cope with heat and water stress, evergreen and deciduous species from hot and arid deserts should adjust their stomatal conductance (g _s) and leaf water potential (Ψ_leaf) regulation in response to changes in soil water availability, high temperatures, and vapour pressure deficits (VPDs). To test whether phenology induces changes in g _s-Ψ_leaf coordination, we tested for associations between 14 leaf traits involved in leaf economics, hydraulics, and stomatal regulation, including minimum seasonal water potential (Ψ_min) and maximum g _s (g _smax), turgor loss point (Ψ_tlp), osmotic potential (Ψ_o), leaf area (LA), and specific leaf area (SLA), across 12 tree species from the Sonoran Desert with contrasting phenology. We found that foliar phenology, leaf hydraulics, and leaf economic traits are coordinated across species and organized along the axis of physiological efficiency and safety in response to temperature and VPD. Evergreens were more drought-tolerant and more restrictive in water use than deciduous species, maintaining lower g _s during the rainy season and lower Ψ_min, Ψ_o, and Ψ_tlp. In contrast, deciduous species were less drought-tolerant, shedding their leaves during the dry season. During the rainy season, they exhibit higher g _s than evergreens, enhancing water transpiration. Moreover, deciduous species, as isohydric plants, showed stricter control over g _s and finer regulation of leaf water potential (Ψ_leaf). Due to their remarkable physiological diversity, desert trees can endure extreme environmental conditions by employing contrasting hydrological strategies.