Differences in branch hydraulic architecture related to the aridity of growing sites and seed sources of coastal Douglas-fir saplings.

To better understand hydraulic adaptations of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) to local climate, we examined genetic (G) and environmental (E) responses of branch hydraulic architecture of 7-year-old saplings from dry and wet climates of origin grown at a relatively dry and a relatively wet common garden site in western Oregon. We sampled 2 years of branch growth from three dry-source and three wet-source families grown at both sites (72 branches, total). Overall, only 4 of the 11 traits had significant genetic (G) effects, whereas 9 traits had significant environmental (E) effects (P  < 0.05). Both dry and wet sources had higher leaf-specific conductance (k _l) at the dry than the wet site, but the values were achieved by different mechanisms and driven by G × E effects for leaf area/sapwood area (A _l/ A _s), shoot length (L), specific conductivity (K _s) and leaf-specific conductivity (K _l). Dry sources achieved higher k _l in the dry site through higher K _l (via a lower A _l/ A _s and no change in K _s) with no difference in L. Wet sources achieved higher k _l at the dry site through no difference in K _l (via no effect on A _l/ A _s, despite decreases in A _l and A _s, and lower K _s) with lower L. Vulnerability to embolism (measured as percentage loss of conductivity at 4 MPa) had no G effect but an E effect, with slightly lower values at the dry site. Specific leaf area had G and E effects, with lower values for the dry sources and site. There were no G or E effects on wood density. The different responses of dry and wet sources to site aridity suggest that populations are differentially adapted to the aridity of growing sites. Population variation in response to aridity should be considered when selecting seed sources for establishing forests for future climates. [ABSTRACT FROM AUTHOR]