© 2000 Heron Publishing—Victoria, Canada
Leaf water relations and stomatal behavior of four allopatric Eucalyptus species planted in Mediterranean southwestern Australia
Don A. White (1), Neil C. Turner (2) and Jeffrey H. Galbraith (1)
1. CSIRO Forestry and Forest Products, Centre for Mediterranean Agricultural Research, Private Bag No. 5, PO Wembley, WA 6913,
Australia / 2. CSIRO Plant Industry, Centre for Mediterranean Agricultural Research, Private Bag No. 5, PO Wembley, WA 6913, Australia / Received October 13, 1999
Summary
In 1986, four allopatric Eucalyptus species (E. camaldulensis Dehnh, E. saligna Smith, E. leucoxylon F. Muell and E. platypus Hook.) were planted together in a 480-mm rainfall zone, in 8-m wide contour belts as part of a plan to minimize waterlogging
and secondary salinization. Throughout 1997, 1998 and 1999, there was significant inter-specific variation in predawn leaf
water potential (Ψpd); however, maximum stomatal conductance (gsm) only differed significantly between species in mid to late summer. Relationships between gsm and Ψpd were significant and showed that stomata of E. camaldulensis were significantly more sensitive to Ψpd, and presumably soil water potential, than stomata of E. leucoxylon or E. platypus. When applied to the Ψpd data, these relationships predicted that gsm, and by inference transpiration, varied much less between species than Ψpd. Diurnal measurements throughout the season confirmed this prediction, and showed that E. camaldulensis and E. saligna avoided drought by gaining access to deeper water, whereas E. leucoxylon and E. platypus maintained greater gsm at a given water stress than E. camaldulensis or E. saligna. Osmotic potentials measured after rehydration and water release curves of the leaves indicated that different mechanisms
accounted for the apparent drought tolerance of E. leucoxylon and E. platypus. In summer, E. leucoxylon reduced osmotic potential at full and zero turgor by similar amounts compared with winter. In summer, E. platypus had a significantly lower bulk elastic modulus and relative water content at turgor loss point than E. camaldulensis, E. saligna or E. leucoxylon. This elastic adjustment resulted in a larger difference between osmotic potential at full and zero turgor in summer than
in winter. The inherently low osmotic potential in E. leucoxylon and elastic adjustment in E. platypus resulted in turgor loss at a similar and significantly lower water potential than in E. camaldulensis or E. saligna. These results have implications for species selection for planting to manage groundwater recharge in areas prone to waterlogging
and secondary salinization.
Keywords:
drought avoidance, drought tolerance, elastic adjustment, groundwater recharge, osmotic adjustment.
