© 1988 Heron Publishing—Victoria, Canada
Drought tolerance, growth partitioning and vigor in eucalypt seedlings and rooted cuttings
Terence J. Blake (1) and Walter Suiter Filho (2)
1. Faculty of Forestry, University of Toronto, Toronto, Ontario, Canada M6S 1A1 / 2. Companhia Agricola E Florestal Sanata Barbara, Av. Brasil 709, Belo Horizonte, MG, Brazil / Received April 20, 1988
Summary
To clarify the physiological basis of productivity differences among rooted cuttings and seedlings of eucalypt species, relationships
between morphology and water relations were examined in 4-month-old seedlings of Eucalyptus grandis W. Hill ex Maiden, E. urophylla S.T. Blake and E. cloeziana F. Muell. and in 4-month-old rooted cuttings of three E. grandis cultivars. Four-month-old seedlings had greater dry weights, lower leaf area/root dry weight (LA/RDW) ratios and lower shoot/root
dry weight (S/R) ratios than 4-month-old rooted cuttings. For all cultivars of E. grandis, tall rooted cuttings, as defined by height at age 4 weeks, had greater dry weights by age 4 months and lower LA/RDW and
S/R ratios than short rooted cuttings. There were differences in height growth, dry matter productivity and relative shoot
and root development among cuttings of different E. grandis cultivars, but these differences were not as great as the differences between short and tall grades of the same cultivar
and between seedlings and cuttings. Consistent with the differences in LA/RDW and S/R ratios, seedlings had higher daytime
water potentials (Ψx) than cuttings, and tall cuttings had higher daytime values of Ψx than short cuttings. Differences in Ψx were also related to stomatal conductance (gwv), which was up to 300% greater in short cuttings than in tall cuttings. Among seedlings, those of E. cloeziana, which had the smallest dry weight at age 4 months, had the highest gwv, whereas those of E. grandis, which had the greatest dry weight at age 4 months, had the lowest gwv. Unlike seedlings and the tall cuttings, short cuttings lost turgor when subjected to drought. The differences observed in
susceptibility to water stress may account in part for the associated differences in dry matter production. Xylem pressure
potential and relative water deficit at zero turgor did not differ significantly among the types of plants studied, which
suggests that differences in growth rates were not the result of differences in dehydration tolerance.
