© 1994 Heron Publishing—Victoria, Canada
Genotypic differences in water use efficiency and 13C discrimination in Eucalyptus globulus
J. Osório (1) and J. S. Pereira (1, 2)
1. Department of Forestry, Instituto Superior de Agronomia, Tapada da Ajuda, 1399 Lisboa codex, Portugal / 2. Author to whom correspondence should be addressed / Received September 24, 1993
Summary
Cuttings of three Eucalyptus globulus Labill. clones (called SM, VC, DG henceforward) were grown for 56 days in 10-l pots in a greenhouse. Every other day, eight
pots of each clone were watered to field capacity (HW treatment), whereas the other eight pots of each clone received only
25% of the water needed to maintain the soil at field capacity (LW treatment). Transpirational water loss, biomass production,
leaf gas exchange and water potential (at predawn and midday) were determined at different times during the experiment. Leaf
tissue formed by the LW plants after the onset of the treatment was analyzed for 13C/12C ratio against the PeeDee Belemnite standard (δ13C). The three clones differed significantly in growth capacity (SM > DG > VC) and in their response to water stress. Even
though leaf water potentials were not significantly modified by withholding water, total biomass and plant leaf area were
affected significantly by soil water deficits by the end of the experiment. The fastest growing clone (SM) was the most affected
by water deficit. Long-term water use efficiency (i.e., biomass per unit of water transpired, WUE) was significantly increased
by water deficit and was positively correlated with δ13C. Long-term WUE was well correlated with the quotient of the daily integrals of carbon assimilation rate and stomatal conductance.
The value of δ13C was negatively correlated with the variables normally positively related with growth, such as specific leaf area (SLA) and
the biomass/intercepted light quotient (ε), and it was positively related to the amount of carbon per unit leaf area, which
is usually negatively correlated with relative growth rate.
Keywords:
biomass production, carbon assimilation, clones, stomatal conductance, transpiration, water stress.
