Morpho-anatomical and physiological traits in saplings of drought-tolerant Mediterranean woody species

Heat and drought events-increasing both in frequency and severity-have led to forest decline, and are a serious threat for the Mediterranean biome. Whereas drought tolerance of adult trees of different Mediterranean species has been widely investigated, this is not the case for saplings and young trees. We analysed correlations and trade-offs among leaf (water potential at the turgor loss point, Psi(tlp), modulus of elasticity, epsilon, osmotic potential at full turgor, pi(0), leaf capacitance, C-leaf_dw, leaf venation, VLA, leaf mass per area, LMA) and stem (wood capacitance and wood density, C-wood and D-wood, stem-specific conductivity and water potential inducing 50% loss of hydraulic conductance) functional traits of saplings for 14 woody species of the Mediterranean flora. The results support previously reported correlations among functional traits known to confer drought tolerance to plants. In particular,Psi(tlp) was positively correlated to pi(0), C-leaf_dw and VLA, while negatively correlated to epsilon and LMA. A highly significant correlation was highlighted between Cwood and Dwood. Overall, we observed surprisingly low symplastic and apoplastic resistance. We identify some easily measurable traits (pi(0) and LMA), which evidence seedlings' ability to cope with drought, and which therefore could be used as proxies in the selection of drought-tolerant saplings for reforestation in Mediterranean areas.