Changes in petiole hydraulic properties and leaf water flow in birch and oak saplings in a CO₂-enriched atmosphere

摘要

Water relations in woody species are intimately related to xylem hydraulic properties. High CO₂ concentrations ([CO₂]) generally decrease transpiration and stomatal conductance (g_s), but there is little information about the effect of atmospheric [CO₂] on xylem hydraulic properties. To determine the relationship between water flow and hydraulic structure at high [CO₂], we investigated responses of sun and shade leaves of 4-year-old saplings of diffuse-porous Betula maximowicziana Regel and ring-porous Quercus mongolica Fisch. ex Ledeb. ssp. crispula (Blume) Menitsky grown on fertile brown forest soil or infertile volcanic ash soil and exposed to 500 μmol CO₂ mol?1 for 3 years. Regardless of species and soil type, elevated [CO₂] consistently decreased water flow (i.e., g_s and leaf-specific hydraulic conductivity) and total vessel area of the petiole in sun leaves; however, it had no effect on these parameters in shade leaves, perhaps because g_s of shade leaves was already low. Changes in water flow at elevated [CO₂] were associated with changes in petiole hydraulic properties.