The variability of branch-level hydraulic properties was assessed across 12 Scots pine populations covering a wide range of environmental conditions, including some of the southernmost populations of the species. The aims were to relate this variability to differences in climate, and to study the potential tradeoffs between traits.
Traits measured included wood density, radial growth, xylem anatomy, sapwood- and leaf-specific hydraulic conductivity (K_S) and K_L), vulnerability to embolism, leaf-to-sapwood area ratio (A_L : A_S), needle carbon isotope discrimination (Δ¹³C) and nitrogen content, and specific leaf area.
Between-population variability was high for most of the hydraulic traits studied, but it was directly associated with climate dryness (defined as a combination of atmospheric moisture demand and availability) only for A_L : A_S, K_L and Δ¹³C. Shoot radial growth and A_L : A_S declined with stand development, which is consistent with a strategy to avoid exceedingly low water potentials as tree size increases. In addition, we did not find evidence at the intraspecific level of some associations between hydraulic traits that have been commonly reported across species.
The adjustment of Scots pine's hydraulic system to local climatic conditions occurred primarily through modifications ofA_L: A_S and direct stomatal control, whereas intraspecific variation in vulnerability to embolism and leaf physiology appears to be limited.