Variation in water use efficiency and δ 13C levels in Eucalyptus grandis clones

Abstract

This study aimed to determine whether the δ 13C levels in the foliage and twigs of four Eucalyptus grandis clones were related to their water use efficiency (WUE). This relationship has previously been demonstrated in a number of herbaceous species but not in mature trees. The study involved accurate measurements of tree trunk growth and water use over a period of 4 months, with subsequent isotopic analysis of mature foliage from the north and south side of the canopy, and young leaves from the top of the canopy. The water use efficiencies were found to vary from 5.97 × 10 −3 to 12.3 × 10 −3 m 3 m −3. Significant differences were observed between clonal-mean water use efficiencies averaged over six sampling periods. The average δ 13C of the mature and young foliage was found to be significantly correlated with WUE. However, the correlation was weak, suggesting that the relationship between δ 13C and WUE is more complex in trees than suggested in the literature on crop plants. It is suggested that differences between sample trees in carbon allocation and leaf-to-air vapour pressure deficits may account for the poor correlation between δ 13C and WUE in the four E. grandis clones studied.