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 (kt) 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 kt, 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.

This work was supported by the Ministry of Innovative Development of the Republic of Uzbekistan (Order No. 109. 2022), by the German Academic Exchange Service (DAAD; Short Term Grants 2022 [57588366]) and by the Samarkand Agroinnovations and Research University, Uzbekistan (Order No. 01/2-86).