Wood Anatomical and Hydraulic Traits of Tamarix Species Across a Large Eurasian Gradient Show a Stronger Climatic Than Phylogenetic Signal

Aim: Tamarisk (Tamarix) is the predominant but taxonomically complex genus of the Tamaricaceae. The morphologically similar shrub or tree species grow in arid, salt-influenced habitats of Eurasia and Africa. We sampled woody shoots of seven species at the eastern margin (NW China; T. ramosissima) and the centre (Uzbekistan; T. hispida) of the Indo-Turanian region as well as at the eastern (Israel; T. aphylla, T. negevensis, T. nilotica) and western margin (southern Spain; T. boveana, T. gallica) of the Mediterranean region, the two diversity centres of the genus. To explore the drivers of intrageneric trait variability, we investigated whether differences in the anatomical-hydraulic wood traits among the species are related to climate or phylogeny. Location: Eurasia. Taxon: Tamarix L. (Tamaricaceae). Methods: We determined features of wood anatomy and calculated the hydraulic conductivity (k_t) and the water potential at 50% loss of hydraulic conductance (P₅₀). We related these traits to climate variables and to the phylogenetic distances among the species. Results: Tamarix nilotica, T. negevensis and T. ramosissima exhibited large conduit areas, large hydraulic diameters and high k_t, whereas the Spanish species T. gallica and T. boveana displayed high wood densities and a small fraction of large conduits. The phylogenetically distant species T. aphylla and T. hispida took intermediate positions. Tamarix ramosissima, which grows in regions with cold winters and hot-dry summers, exhibited the most negative P₅₀ values, indicative of a low susceptibility to a failure of the water-conducting system. Trait differences among the species were unrelated to the species' phylogenetic relatedness but correlated with climate variables. Main Conclusions: Despite strong similarity in morphology and habitat preferences, Tamarix species displayed significant differences in their anatomical-hydraulic traits. These differences were related to climate conditions rather than phylogeny and are indicative of specific local adaptations to environmental conditions.