Acclimation potential of seedlings of six non-pioneer, North Queensland rainforest tree species
(Diploglottis diphyllostegia, Flindersia brayleyana, Dysoxylum schgneri, Prunus turnerana, Neisosperma
poweri and Castanospora alphandii) were evaluated in three different light regimes. The seedlings were
grown from seeds and raised in 37, 10 and 2.5% photosynthetically active radiation (PAR) of full
sunlight in a shade house. Plants were harvested at 1, 4, and 15 months after germination. At 4 months,
for each species, one-third of the seedlings in each light environment were transferred to each of the
two other light environments. The remaining one-third stayed in the same light environment and formed
the control. The control seedlings of all species showed a marked response to increasing PAR: relative
growth rate (RGR) and total biomass were low in the 2.5% PAR level, increased in the 10% PAR
level and were maximal in the 37% PAR level, except for Neisosperma. The seedlings in the 25%
PAR level showed a typical shade plant morphology with a high leaf area ratio, low root-shoot ratio
and low specific leaf weight. For seedlings of Dysoxylum and Prunus, a change in light regime from
37% PAR to 2.5% PAR resulted in negative relative growth rates. Eleven months after transfer, many
growth characteristics still showed significant initial × final light environment interactions, an indication
of incomplete adjustment. Acclimation to increasing light availability was faster than acclimation to
decreasing light availability. On the basis of biomass allocation patterns (root-shoot ratio, leaf area
ratio and specific leaf weight), the six species could not be differentiated under the three light regimes
and their dynamics. However, using RGR as a relative measure of carbon economy, it was possible
to differentiate the species in their acclimation ability to decreased but not to increased irradiance.
It was concluded that, for non-pioneer species, acclimation potential may be more related to physiological
than to morphological plasticity.
Light acclimation potential and carry-over effects vary among three evergreen tree species with contrasting patterns of leaf emergence and maturation