© 2005 Heron Publishing—Victoria, Canada
Growth efficiency increases as relative growth rate increases in shoots and roots of Eucalyptus globulus deprived of nitrogen or treated with salt
Craig Macfarlane (1, 2), Lee D. Hansen (3), Justine Edwards (1), Donald A. White (4) and Mark A. Adams (5)
1. School of Plant Biology (M090), Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling
Highway, Crawley, WA 6009, Australia / 2. Corresponding author (cmacfarl@cyllene.uwa.edu.au) / 3. Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602, USA / 4. CSIRO Forestry and Forest Products, Centre for Environment and Life Sciences, P.O. Box 5 Wembley, WA 6913, Australia / 5. The Centre of Excellence in Natural Resource Management, The University of Western Australia, 35 Stirling Highway, Crawley,
WA 6009, Australia / Received May 14, 2004; accepted September 3, 2004; published online March 1, 2005
Summary
We used calorimetry to test whether there is a single general relationship between growth and respiration in shoots and roots
of Eucalyptus globulus Labill. seedlings when stressed, irrespective of the type or severity of stress. We found that nitrogen (N) deprivation and
salt treatment had no effect on the relationship between growth and respiration and little effect on absolute rates of respiration.
Carbon-conversion efficiency (εC) ranged from 0.7 to 0.9 for specific growth rates (RSG) greater than 0.3 day–1. Above an RSG of 0.1 day–1, εC decreased gradually with decreasing RSG and between an RSG of 0– 0.1 day–1, εC decreased rapidly. We conclude that the relationship between εC and RSG is not greatly affected by salt or N-deprivation stresses. Relationships between gross productivity and εC may be generally applicable, in which case they could improve on the “flat-tax” approach to modeling net primary productivity
from gross productivity while avoiding the complexity of more explicit models of plant respiration. However, the relationship
between gross productivity and εC was sensitive to temperature and the effect of temperature on εC thus requires further investigation. Nitrogen deprivation caused large decreases in leaf area and shoot to root ratio, and
mature leaves of N-deprived plants had lower intrinsic water-use efficiencies than leaves of plants well supplied with nutrients.
Nitrogen deprivation increased apical dominance and most of the reduction in leaf area was the result of fewer secondary branches,
although leaf size was also reduced. Our results suggest that N deprivation reduces productivity primarily by reducing sink
size, rather than sink activity, and that apical dominance may be an important mechanism for maintaining adequate εC in resource-limited conditions.
Keywords:
apical dominance, calorimetry, enthalpy balance model, growth-and-maintenance paradigm, respiratory quotient, sink strength.
