Effects of soil water availability on water use efficiency of Eucalyptus cloeziana and Eucalyptus argophloia plants

Abstract

Effects of soil water availability on transpiration efficiency (WUET), instantaneous water use efficiency (WUEi) and carbon isotope composition (δ13C) were investigated in 7-month-old plants of humid coastal (Gympie) and dry inland (Hungry Hills) provenances of Eucalyptus cloeziana F.Muell. and in a dry inland provenance of E. argophloia Blakely (Chinchilla), supplied with 100 (W100), 70 (W70) and 50% (W50) of their water requirements. At W100, WUET of the three provenances were not significantly different but as available soil moisture decreased, E. argophloia produced greater biomass and demonstrated significantly higher WUET than either E. cloeziana provenance. Midday WUEi was not significantly affected by watering regime within each provenance but was lowest in E. argophloia. A decrease in soil water availability caused a consistent increase in δ13C values in all three provenances; however, δ13C values of E. argophloia in all three water regimes were significantly lower than those of E. cloeziana provenances, which did not differ significantly from each other. For all three provenances, δ13C was not correlated with WUEi but height and root collar diameter were negatively correlated to δ13C. There was little evidence of differences in δ13C, WUET and WUEi between E. cloeziana provenances but clear differences between E. cloeziana and E. argophloia. The high WUET, low WUEi and low δ13C for E. argophloia may have implications in the selection of Eucalyptus provenances for commercial forestry in low-rainfall regions.