The Temperature-Dependence of Photosynthesis of Some Australian Temperate Rainforest Trees and its Biogeographical Significance

Abstract

The effect of temperature on photosynthesis was examined in several species of Australian temperate rainforest trees to test three hypotheses regarding the distribution and evolution of the species. The results suggest that changing temperatures in south-eastern and eastern Australia during the Tertiary may have affected species distribution and influenced evolution. For Nothofagus, N. moorei is closest to the ancestral species and has a higher optimum temperature for photosynthesis than the derived species N. cunninghamii. It is hypothesized that this difference is the result of the evolution occurring with declining temperatures in south- eastern Australia during the Tertiary, when the ancestral species evolved into N. cunninghamii. The three Eucryphia species tested do not exhibit such a marked trend, but vary considerably in their relative rates of photosynthesis above and below their optimum temperature for photo- synthesis. The species restricted to northern temperate rainforests which have no close relatives in the southern temperate forests (Ceratopetalum apetalum and Doryphora sassafras) have a substantially higher optimum temperature for photosynthesis than the southern species. These results are consistent with the computer-predicted distributions of the species based on the climate profiles of their known distributions.