Response of seedlings of two Eucalyptus and three deciduous tree species from Ethiopia to severe water stress

The responses of the seedlings of three deciduous species, viz. Cordia africana Lam., Croton macrostachyus Del., Millettia ferruginea (Hochst.) Baker, and two eucalypts, viz. Eucalyptus camaldulensis Dehnh. and Eucalyptus globulus Labill to severe water stress were studied in a glasshouse for a period of 12 days. Severe water stress (drought) was induced by withholding water. The study found that E. globulus and E. camaldulensis were more vulnerable to severe water stress compared to the three deciduous species examined. Severe water stress resulted in dehydration and dieback of both E. camaldulensis and E. globulus seedlings within 7 days. In the deciduous tree species studied, severe water stress resulted in leaf shedding. Only the youngest leaves were retained by the deciduous species throughout the severe water-stress period. Mid-day depression in stomatal conductance and photosynthesis was highest for C. africana followed by C. macrostachyus. Of the five tree species studied, M. ferruginea had the highest water potential and relative water content, as well as the lowest stomatal conductance throughout the water-stress period. In the well-watered group, both E. globulus and E. camaldulensis had higher stomatal conductance, photosynthetic rate and water loss as compared to the three deciduous species. Three mechanisms of coping with water deficit were identified: (1) stomatal closure in C. africana and C. macrostachyus; (2) reduction of leaf area in the deciduous species; and (3) change in leaf orientation in M. ferruginea. (C) 2004 Elsevier B.V. All rights reserved.