Estimation of drought-related limitations to mid-rotation aged plantation grown Eucalyptus globulus by phloem sap analysis

Previous research has shown that carbon isotope signatures (Δ13C) may correlate well with water status in 1–2 years old, plantation grown Eucalyptus globulus. Here we investigate this relationship for mid-rotation aged (5 years) trees and whether a simple field determination of phloem sugar concentrations is a reliable surrogate for Δ13C. We sampled six plantations covering much of the climatic range of E. globulus plantations in Australia (average annual rainfall 618–1094 mm). We found significant correlations between phloem Δ13C and phloem sugar concentrations across and within plantations. Both parameters were also correlated with a climate wetness index. We thus conclude that phloem sugar concentration is a useful surrogate for Δ13C and hence water status of mid-rotation E. globulus. We also observed strong correlations of phloem Δ13C and phloem sugar concentrations with growth across all plantations, providing some confirmation that water limits growth of E. globulus at a larger scale. This relationship was much weaker or absent within plantations, suggesting that factors other than water supply contribute significantly to growth limitations at smaller (within-plantation) scales.