Photosynthetic and growth responses to different light regimes of the major canopy species of Tasmanian cool temperate rainforest

Abstract

AbstractSeedlings of the cool temperate rainforest tree species, Nothofagus cunninghamii, Atherosperma moschatum, Eucryphia lucida, Phyllocladus aspleniifolius, Lagarostrobos franklinii and Athrotaxis selaginoides, were grown in various light regimes and their instantaneous lightdependence curves and relative growth rates were measured. A. moschatum had the highest relative growth rate of all species in heavy shade, and its light‐dependence curves were also characteristic of a relatively shade‐tolerant species. A. selaginoides and L. franklinii seedlings raised in heavy shade had low instantaneous light compensation points but their growth rates were not distinct from that of N. cunninghamii. The maximum relative growth rate of the gymnosperms was low due to a low specific leaf area and leaf area ratio, although the maximum rates of photosynthesis on a leaf area basis were similar to N. cunninghamii and E. lucida. The low leaf area ratio and specific leaf area affected both the relative growth rate and the growth light compensation point. Although in the heaviest shade treatment there was no difference in growth rate between N. cunninghamii, E. lucida, L. franklinii and A. selaginoides, in moderate shade treatments N. cunninghamii had a higher relative growth rate than the gymnosperms and a higher maximum rate of photosynthesis on a leaf dry weight basis than all species when raised in semi‐shaded natural light conditions. These species commonly occur in mixture in Tasmanian cool temperate rainforest and these results are discussed in terms of forest dynamics.