Genotypic differences in growth and stomatal morphology of Southern Beech,Nothofagus cunninghamii, exposed to depleted CO2 concentrations

Nothofagus cunninghamii (Hook.) Oerst. clones of four different genotypes f rom Mt Field National Park, Tasmania were grown at both current (similar to 370 mu mol mol(-1)) and depleted (similar to 170 mu mol mol(-1)) CO2. Grow th was significantly less in the lower [CO2] treatment in all genotypes. Th e amount of growth reduction caused by low [CO2] depended strongly upon gen otype and varied from less than 30% to greater than 75% reduction of whole plant biomass when compared to growth at current [CO2]. Specific leaf area was significantly greater in all plants grown in reduced [CO2], whereas ind ividual leaf area was not significantly affected by [CO2]. The direction an d magnitude of the response of stomatal index, stomatal density and epiderm al cell density to [CO2] was strongly dependent upon genotype. [CO2] had a significant effect on the length of the stomatal pore, but the magnitude of the effect (similar to 3%) was trivial compared to changes in stomatal den sity (up to 20%). There was a significant (P < 0.01) and positive relations hip between the response of stomatal density and growth response of a genot ype. Therefore, we propose that the response of stomatal density to [CO2] c ontrols the relative growth response of N. cunninghamii and that this respo nse is highly dependent upon genotype.