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 (gs) and leaf water potential (Ψleaf) regulation in response to changes in soil water availability, high temperatures, and vapor pressure deficits (VPD). To test if phenology induces changes in gs - Ψleaf coordination, we tested for associations between 14 leaf traits involved in leaf economics, hydraulics, and stomatal regulation, including minimum seasonal water potential (Ψmin) and maximum gs (gsmax), turgor loss point (Ψtlp), osmotic potential (Ψo), leaf area (LA), and specific leaf area (SLA), across 12 tree species from the Sonoran Desert (SD) 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 gs during the rainy season and lower Ψmin, Ψo, and Ψtlp. In contrast, deciduous species were less drought-tolerant, shedding their leaves during the dry season. During the rainy season, they exhibit higher gs than evergreens, enhancing water transpiration. Moreover, deciduous species, as isohydric plants, showed stricter control over gs and finer regulation of leaf water potential (Ψleaf). Due to their remarkable physiological diversity, desert trees can endure extreme environmental conditions by employing contrasting hydrological strategies.