Physiological responses to water stress in Eucalyptus cloeziana and E. argophloia seedlings

Effects of water stress duration and intensity on gas exchange and leaf water potential were investigated in 7-month-old seedlings of a humid coastal provenance (Gympie) and a dry inland (Hungry Hills) provenance of E. cloeziana F. Muell. and in a dry inland (Chinchilla) provenance of E. argophloia Blakely supplied with 100% (T100), 70% (T70), 50% (T50) of their water requirements, or were watered only after they were wilted at dawn (T0). Seedlings of E. argophloia had the highest midday net photosynthetic rate (A), stomatal conductance (gs), stomatal density and predawn leaf water potential (Ψpd) in all treatments. The E. cloeziana provenances did not differ in these attributes. The T70 and T50 treatments caused reductions in A of 30% in E. argophloia, and 55% in the E. cloeziana provenances. Under the T0 treatment, E. argophloia maintained higher rates of gas exchange at all levels of water stress than E. cloeziana provenances. The estimates of Ψpd and midday water potential (Ψmd) at which plants remained wilted overnight were respectively: -2.7 and -4.1 MPa for E. cloeziana (humid), -2.8 and -4.0 MPa for E. cloeziana (dry) and, -3.7 and -4.9 MPa for E. argophloia. Following stress relief, both A and gs recovered more quickly in E. argophloia and in the dry provenance of E. cloeziana than in the humid provenance. We conclude that E. argophloia is more drought tolerant and has a potential for cultivation in the humid and semi humid climates, whilst E. cloeziana has greater potential in the humid subtropical climates. © Springer-Verlag 2004.