How are physiological responses to drought modulated by water relations and leaf economics' traits in woody plants?

Species' drought resistance is determined by a combination of multiple traits and their plastic response. How-ever, a clear understanding of how these traits are coordinated and modulate plant responses to drought is still lacking.Here we used a water exclusion experiment on 20 Mediterranean woody species to evaluate a new framework to study plant drought responses, in which relatively constant functional traits modulate the physiological re-sponses to a given drought exposure. In particular, we assessed how the response of stomatal conductance (Gs), leaf relative water content (RWC) and leaf water potential difference (AT) to leaf predawn water potential (Tpd) were modulated by commonly used functional traits. The latter included hydraulic and water relations attributes such as turgor loss point in leaves (Ttlp), vulnerability to xylem embolism in stems (T50), hydraulic conductivity per unit sapwood (Ks), hydraulic conductivity per unit leaf area (Kl, hydraulic sufficiency) and Huber value (Hv), as well as specific leaf area (SLA) as a proxy for the leaf economics spectrum.Our results show that functional traits are highly coordinated, defining two main axes: the first related to drought tolerance and resource-use strategies and the second characterising the hydraulic sufficiency of leaves. These two axes, as well as many of the underlying functional traits, showed a significant interaction with Tpd in explaining physiological responses to drought, thus modulating Gs, RWC, and AT responses. Drought-tolerant species showed a less stringent regulation of water use and leaf water potential but were more effective at regulating leaf RWC. Also, the leaf water potential at turgor loss (Ttlp) emerged as an important trait orches-trating plant responses to drought.This study highlights that a clear separation between slow-varying traits (Ttlp, T50, Ks, Kl, Hv, SLA), physio-logical responses (Gs, RWC, AT) and tissue-level exposure to drought (Tpd) improves our understanding of plant drought resistance strategies.