PHOTOSYNTHETIC CHARACTERISTICS OF FLINDERSIA-BRAYLEYANA AND CASTANOSPERMUM-AUSTRALE FROM TROPICAL LOWLAND AND UPLAND SITES

Photosynthetic responses to temperature, light and carbon dioxide part ial pressure were studied in two-year-old Flindersia brayleyana F. Mue ll. and Castanospermum australe Cunn. & C. Fraser ex Hook. growing on coastal lowland and upland rainforest sites in tropical Queensland, Au stralia. Climatic conditions ranged from moist and cool (17-19 degrees C) to dry and warm (22-24 degrees C). The optimum temperature for pho tosynthesis was 23.7-25.6 degrees C for C. australe and 21.2-24.6 degr ees C for F. brayleyana. Mean maximum rate of electron transport for e ach species did not differ between sites but was higher (60-62 mu mol m(-2) s(-1)) in F. brayleyana than in C. australe (42-44 mu mol m(-2) s(-1)). Ribulose-bisphosphate carboxylation rate did not differ signif icantly between sites or species. Maximum rates of photosynthesis at 1 000 mu Pa Pa-1 CO2 did not differ significantly between sites for each species, but did differ significantly between species. At 350 mu Pa P a-1 CO2, photosynthetic light use efficiencies of F. brayleyana and C, australe were 0.05 and 0.015, respectively, at the upland site, and t he corresponding values at the lowland site were 0.025 and 0.05. In C. australe, these differences were reflected in significantly greater m aximum rates of photosynthesis at 350 mu Pa Pa-1 CO2 at the lowland si te than at the upland site (5.2 versus 3.3 mu mol m(-2) s(-1)).