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 from Mt Field National Park, Tasmania were grown at both current (~370 μmol mol-1) and depleted (~170 μmol mol-1) CO2. Growth was significantly less in the lower [CO2] treatment in all genotypes. The amount of growth reduction caused by low [CO2] depended strongly upon genotype 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 individual leaf area was not significantly affected by [CO2]. The direction and magnitude of the response of stomatal index, stomatal density and epidermal 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 (~3%) was trivial compared to changes in stomatal density (up to 20%). There was a significant (P < 0.01) and positive relationship between the response of stomatal density and growth response of a genotype. Therefore, we propose that the response of stomatal density to [CO2] controls the relative growth response of N. cunninghamii and that this response is highly dependent upon genotype.