Physiological responses of Eucalyptus nitens × nitens under experimentally imposed water stress

Abstract

This study reports on how a cold- and frost-tolerant clone of Eucalyptus nitens × nitens responds to drought stress. The aim was to identify physiological traits that contribute to drought acclimation. Macropropagated saplings were grown in a climate-controlled greenhouse in pots filled with coarse river sand supplied with a slow-release fertiliser. One group of plants was kept regularly watered (control), and another group was subjected to four cycles of water stress (drought) whereby water was withheld for periods lasting 6, 10, 10 and 14 d, with 4 d of regular watering (recovery) inbetween. A drought cycle was terminated once saplings showed signs of wilting. Daily responses in stomatal conductance (g s) were similar between control and drought treatments, except on the day of termination of the cycle, when g s was significantly depressed in droughted plants. During the fourth and most severe drought cycle, there was a physiological adaptation to water stress because g s was similar between control and droughted plants. Stomatal conductance was significantly positively correlated with volumetric soil moisture content in the drought treatment, but not in the control treatment. Electron transport capacity (J max) increased during each drought cycle, and the increase was significant during the fourth cycle. Other parameters derived from A/c i response curves were similar between the treatments. Under experimentally imposed water stress, E. nitens × nitens reduced leaf area, increased assimilate rate per unit leaf area, and maintained high stomatal conductance until leaves wilted. After 46 d droughted plants had accumulated half the biomass of control plants. Therefore, a cold- and frost-tolerant clone of E. nitens × nitens may be tolerant to drought stress but at a reduced growth rate because of reduced leaf area.