Leaf osmotic potential of Eucalyptus hybrids responds differently to freezing and drought, with little clonal variation
Andrew N. Callister (1, 2, 3), Stefan K. Arndt (1), Peter K. Ades (1), Andrew Merchant (4), Douglas Rowell (1) and Mark A. Adams (4)
1. School of Forest and Ecosystem Science, University of Melbourne, Water Street, Creswick, VIC 3363, Australia / 2. Present address: ITC Forestry, P.O. Box 1421, Albany, WA 6331, Australia / 3. Corresponding author () / 4. Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia / Received October 12, 2007; accepted April 4, 2008; published online June 2, 2008
Summary
Concentrations of solutes, and thus leaf osmotic potential (Ψπ), often increase when plants are subject to drought or sub-zero (frost) temperatures. We measured Ψπ and concentrations of individual solutes in leaves of 3-year-old Eucalyptus camaldulensis Dehn., E. globulus Labill., E. grandis W. Hill ex Maid. and 29 hybrid clones on a site subjected to both summer drought and winter frost. We sought to characterize
seasonal and genetic variations in Ψπ and to determine whether Ψπ or leaf turgor is related to bole volume increment. Leaf osmotic potential at full turgor (Ψπ(100)) was 0.7 MPa more negative in winter than in late summer, and this trend was uniform across genotypes. Soluble carbohydrates
were confirmed as key contributors to Ψπ, accounting for 40–44% of total osmolality. The seasonal trend in Ψπ(100) was facilitated by changes in leaf morphology, such as reduced turgid mass:dry mass ratio and increased apoplastic water
fraction in winter. Cell wall elasticity increased significantly from winter to summer. Our results suggest that elastic adjustment
may be more important than osmotic adjustment in leaves exposed to drought. Although Ψπ(100) was a reasonable predictor of in situ osmotic potential and turgor, we found no relationship between any physiological trait
and bole volume increment. Clone-within-family variation in Ψπ(100) was small in both summer and winter and was unrelated to bole volume increment. We conclude that, for the study species,
tree improvement under water-limited conditions should concentrate on direct selection for growth rather than on indirect
selection based on osmotic potential.
