Variability in growth, carbon isotope composition, leaf gas exchange and hydraulic traits in the eastern mediterranean cedars Cedrus libani and C. brevifolia

Four Turkish provenances and five Lebanese provenances of Cedrus libani A. Rich. and one Cypriot provenance of C. brevifolia Henry were compared during the third year of growth in a controlled-climate greenhouse after exposure to a well-watered or moderate-drought treatment. Effects of treatment on CO2 assimilation (A), stomatal conductance (gs), 13C isotope composition (δ13C), growth and biomass were assessed. Hydraulic conductivity and shoot vulnerability to cavitation were measured in well-watered plants only. The Lebanese provenances of C. libani had the highest growth rates, but were the most sensitive to drought. The Turkish provenances of C. libani showed moderate growth rates and moderate drought sensitivity. Cedrus brevifolia had the lowest growth rate and was least sensitive to drought. For each provenance, mean biomass values were positively correlated with δ13C and intrinsic water-use efficiency (A/gs), and negatively correlated with gs. Drought reduced growth and favored carbon storage in roots, increasing the ratio of root biomass to aboveground biomass. The drought treatment increased δ13C and A/gs. Specific hydraulic conductivity (Ks) was similar for the provenance groups, whereas leaf-specific conductivity (Kl) was lower in the Lebanese provenances than in the other provenances. Within each pro