© 2004 Heron Publishing—Victoria, Canada
Responses to water stress in two Eucalyptus globulus clones differing in drought tolerance
F. Costa e Silva (1, 2), A. Shvaleva (1, 3), J. P. Maroco (3, 4), M. H. Almeida (1), M. M. Chaves (1, 3) and J. S. Pereira (1)
1. Instituto Superior de Agronomia, Departamento de Engenharia Florestal, Tapada da Ajuda 1349-017 Lisbon, Portugal / 2. Corresponding author (filipecs@isa.utl.pt) / 3. Lab. de Ecofisiologia Molecular, IBET-ITQB, Apt.12 Oeiras 2784-505, Portugal / 4. Instituto Superior de Psicologia Aplicada, Rua Jardim do Tabaco, 44 1149-041 Lisbon, Portugal / Received July 16, 2003; accepted January 26, 2004; published online August 2, 2004
Summary
We evaluated drought resistance mechanisms in a drought-tolerant clone (CN5) and a drought-sensitive clone (ST51) of Eucalyptus globulus Labill. based on the responses to drought of some physiological, biophysical and morphological characteristics of container-grown
plants, with particular emphasis on root growth and hydraulic properties. Water loss in excess of that supplied to the containers
led to a general decrease in growth and significant reductions in leaf area ratio, specific leaf area and leaf-to-root area
ratio. Root hydraulic conductance and leaf-specific hydraulic conductance decreased as water stress became more severe. During
the experiment, the drought-resistant CN5 clone maintained higher leaf water status (higher predawn and midday leaf water
potentials), sustained a higher growth rate (new leaf area expansion and root growth) and displayed greater carbon allocation
to the root system and lower leaf-to-root area ratio than the drought-sensitive ST51 clone. Clone CN5 possessed higher stomatal
conductances at moderate stress as well as higher hydraulic conductances than Clone ST51. Differences in the response to drought
in root biomass, coupled with changes in hydraulic properties, accounted for the clonal differences in drought tolerance,
allowing Clone CN5 to balance transpiration and water absorption during drought treatment and thereby prolong the period of
active carbon assimilation.
Keywords:
acclimation, allocation, hydraulic properties, root growth, water stress.
