Productivity, carbon isotope discrimination and leaf traits of trees of Eucalyptus globulus Labill. in relation to water availability

The stand basal area, carbon isotope discrimination (Delta) in tree rings and leaves, leaf area index and leaf traits of trees were measured in 6- to 8-year-old stands of Eucalyptus globulus Labill. across a gradient of rainfall of 600-1400 mm year(-1) in south-western Australia to better understand the importance of leaf traits and gas-exchange as determinants of stand productivity. Delta ranged from 17parts per thousand to 21parts per thousand. Delta and basal area were highly, positively correlated with each other and the ratio of mean annual rainfall to potential evaporation (P/PE). Leaf area index, soil water holding capacity and leaf nitrogen content were only weakly correlated with basal area. Delta and P/PE were negatively correlated with leaf nitrogen content. Delta was negatively correlated with leaf density but positively correlated with specific leaf area. This is consistent with the theory that larger leaf nitrogen content and smaller specific leaf area are associated with increased photosynthetic capacity and increased leaf-scale water-use-efficiency, and that Delta is influenced by mesophyll conductance. It is concluded that canopy conductance is a more important determinant of growth in water-limited conditions than either leaf area index or leaf traits in fertilized stands of E. globulus. Water availability was dictated more by rainfall than soil type.