Juvenile and adult leaves of heteroblastic Eucalyptus globulus vary in xylem vulnerability

Key message Comparing juvenile and adult shoots of Eucalyptus globulus reveals that juvenile leaves are more vulnerable to hydraulic failure than adults while stems show no significant differences. Understanding variation in the susceptibility for xylem tissue to cavitate and lose its function during water stress exposure is critical for predicting plant mortality during drought. An increasing number of studies examine variation in xylem vulnerability to water-stress-induced damage among species, but very few studies explore variation associated with ontogeny and development. Here, we assess stem and leaf vulnerability to cavitation in the heteroblastic tree species Eucalyptus globulus using a non-invasive optical technique to measure the accumulation of air embolisms during dehydration. No significant difference between the vulnerability of stem xylem was found between juvenile and adult stems, but the xylem of juvenile leaves was more susceptible to cavitation during dehydration than adult leaves. Analysis of vessel diameters indicates differences in maximum vessel diameter but little differences in hydraulically weighted mean vessel diameter. The results are discussed in context of similar studies that compare juvenile and adult plants, as well as potential anatomical and functional trade-offs associated with phase change and growth in E. globulus , which presents a complex relationship across its broad distribution.