Growth and water use of Eucalyptus camaldulensis and E. occidentalis on a saline discharge site near Wellington, NSW, Australia

Abstract

Growth and water use of 7-year-old Eucalyptus camaldulensis and 6-year-old Eucalyptus occidentalis were measured on a saline discharge site near Wellington, New South Wales, Australia. These two species were included in species evaluation trials established on a salinity gradient to determine species salt tolerance. E. occidentalis grew better than E. camaldulensis on saline soil and demonstrated less growth reduction with increasing root zone salinity. For E. camaldulensis, a 10% reduction in height growth was evident when the mean root zone salinity (expressed as the electrical conductivity of a saturated soil paste, EC e), was as low as 2 dS m −1. For E. occidentalis, a 10% reduction in height growth was only evident at a root zone salinity of ca. 10 dS m −1. Similar responses to salinity were found for stem diameter and estimated crown volume. There was no significant difference in transpiration rate per unit of leaf area between four E. camaldulensis trees on non-saline soil (EC e ca. 0.5 dS m −1) and three E. camaldulensis trees on moderately saline soil (EC e ca. 4.5 dS m −1) over a 5 month period. On all but 2 days out of a 3 month period, the transpiration rate per unit of leaf area did not differ significantly between three E. camaldulensis and three E. occidentalis trees on moderately saline soil (EC e ca. 4.5 dS m −1 for E. camaldulensis and 7.1 dS m −1 for E. occidentalis). Differences in transpiration rates per unit of leaf area were small, compared to differences in the average area of leaves per tree. The mean leaf area was only 10 m 2 for six E camaldulensis trees (age 7 years) on moderately saline soil compared with 26 m 2 for six trees of the same provenance on non-saline soil, and 20 m 2 for six E. occidentalis trees (age 6 years) on moderately saline soil. Hence, E. camaldulensis on non-saline soil used more water per tree than either species growing on moderately saline soil. On moderately saline soil, E. occidentalis used twice as much water per tree as E. camaldulensis trees a year older.