Potential of evolutionary adaptation of Douglas fir (Pseudotsuga menziesii Franco.) to drought: role of resistance to cavitation, xylem microdensity and pit anatomical traits

International audience

English. Several turn-of-the-20th-century diebacks have shown that French Douglas-fir was vulnerable to drought. Whether the Douglas-fir forests can adapt to the new warmer and dryer climate is a key concern in France. We estimated variation of resistance to cavitation traits of a set of Washington, Oregon and Californian provenances in two common garden experiments located in the south of France. We studied the relationships between resistance to cavitation, xylem microdensity and pit anatomy in the trunk and branches. We found that climatic selection pressure in the natural area has shaped local adaptation for resistance to cavitation, microdensity and pit's anatomy. Inland California provenances tend to be significantly more cavitation resistant, with a denser latewood and safer pits than coastal Californian, then Washington and Oregon provenances. However, we also found significant within region variation that could not be explained by the available climatic data. We found different structure-functions relationships, according to the observation level (tree or provenance) and the tree part (trunk or branch). For example, at the individual level, the most cavitation-resistant trees have branches with denser latewood and smaller pit aperture, while at the provenance level, the most cavitation resistant provenances have less dense wood in both trunk and branches, and safer pits. Overall, we conclude that there is a potential for evolutionary adaptation for resistance to drought in Douglas-fir, available at different levels, individual and provenance. However, in a tree improvement context, the complex network of relationships among the resistance to cavitation, the microdensity and the anatomy traits should be carefully monitored in order to avoid possible unfavourable correlative response to selection.