© 1993 Heron Publishing—Victoria, Canada
Growth of Eucalyptus marginata (Jarrah) seedlings in a greenhouse in response to shade and soil temperature
G. L. Stoneman (1, 2) and B. Dell (1)
1. Biological and Environmental Sciences, Murdoch University, Murdoch, WA 6150, Australia / 2. Department of Conservation and Land Management, Research Centre, Como, WA 6152, Australia / Received July 3, 1992
Summary
The effects of shade and soil temperature on growth of Eucalyptus marginata Donn ex Sm (jarrah) seedlings were studied in greenhouse experiments. Plant dry weight and that of all plant parts declined
in response to shade, as did root/shoot ratio. Plant leaf area was less in unshaded plants than in plants grown in shade,
and specific leaf area increased with shade. Unshaded seedlings had a higher light-saturated rate of photosynthesis, a higher
light compensation point and a higher light saturation point than seedlings grown in 70% shade. The relationship between plant
dry weight and leaf dry weight was independent of shading, whereas the relationship between plant dry weight and plant leaf
area was
dependent on shading. Therefore, leaf dry weight may be a better predictor of biomass production than leaf area in forest
stands where shade is likely to affect growth significantly.
Soil temperature had a significant effect on the growth of all plant parts except cotyledons. Total plant growth and shoot
growth were maximal at a soil temperature of 30 °C, but root growth had a slightly lower temperature optimum such that the
root/shoot ratio was highest at 20 °C. Roots grown at 15 °C were about 30% shorter per unit of dry weight than roots grown
at 20 to 35 °C.
We conclude that increases in irradiance and soil temperature as a result of overstory removal in the forest will cause significant
increases in growth of E. marginata seedlings, but these increases represent a relatively small component of the growth response to overstory removal.
Keywords:
photosynthesis, leaf area, root to shoot ratio, specific leaf area.
