Genetic variation of xylem hydraulic properties shows that wood density is involved in adaptation to drought in Douglas-fir (Pseudotsuga menziesii (Mirb.))

Introduction Relationships between wood density and hydraulic efficiency and safety (hydraulic specific conductivity and vulnerability to cavitation, respectively) could clarify the physiological process explaining the impact of density on fitness. We have used new, relatively high-throughput phenotyping methods to estimate genetic variation of wood hydraulic specific conductivity (k (s)) and vulnerability to cavitation (VC) as an important step toward demonstrating the adaptive value of wood density. Objective The first aim of this study is to test if, in Douglas-fir, there is a relationship between wood hydraulic properties (k (s) and VC) and wood density. The second objective is to estimate genetic variation of wood k (s) and VC. These results could aid understanding of the role of wood density in the hydraulic properties of xylem and may clarify the role of wood density in adaptation to drought. Results Many significant relationships were found between wood density and wood hydraulic properties at clone and tree level, as well as significant genetic variation for k (s) and VC. We have also found positive correlations between tree height, specific conductivity and vulnerability to cavitation, but no relation was found between radial growth and hydraulic variables. Conclusions Our results suggest that wood density has an adaptive value and that microdensity can be used to study adaptation to drought in Douglas-fir. The novel methods used to measure k (s) and VC proved to be interesting alternatives for localized measurement of wood hydraulic properties and were compatible with a robust estimation of genetic variation.