Studies on the Light Compensation Point of Eucalyptus regnans F. Muell

Abstract

The light compensation point of detached leaves, shoots and intact seedlings of Eucalyptus regnans was studied in terms of gas exchange and growth analysis. The instantaneous compensation point (Ic) of shoots and leaves increased with temperature and with plant age. The shade tolerance of species in the E. regnans mature forest can be correlated with the value of Ic, at 20°C. The growth compensation point (Ic(gr) for young seedling stages was relatively constant in terms of the proportion of outside daylight (c. 1.4%) but in terms of radiometric energy levels it fell from 0.35 to 0.07 MJ m-2 d-2 as the mean temperature fell seasonally from 23°C in summer to 12° in winter. No difference occurred between the Ic(gr) compensation points of two-leaf and 10-leaf seedlings, although there was extensive die-back in the terminal shoots of the larger plants at very low light intensities. The implications of compensation point changes in forest regeneration are discussed.