Altitude of origin influences stomatal conductance and therefore maximum assimilation rate in Southern Beech, Nothofagus cunninghamii

Gas exchange measurements were made on saplings of Southern Beech, Nothofag us cunninghamii (Hook.) Oerst. collected from three altitudes (350, 780 and 1100 m above sea level) and grown in a common glasshouse trial. Plants wer e grown from cuttings taken 2 years earlier from a number of plants at each altitude in Mt Field National Park, Tasmania. Stomatal density increased w ith increasing altitude of origin, and stomatal conductance and carbon assi milation rate were linearly related across all samples. The altitude of ori gin influenced the stomatal conductance and therefore carbon assimilation r ate, with plants from 780 m having a greater photosynthetic rate than those from 350 m. The intercellular concentration of CO2 as a ratio of external CO2 concentration (c(i)/c(a)) was similar in all plants despite the large v ariation in maximum stomatal conductance. Carboxylation efficiency was grea ter in plants from 780 m than in plants from 350 m. Altitude of origin has a strong influence on the photosynthetic performance of N. cunninghamii pla nts even when grown under controlled conditions, and this influence is expr essed in both leaf biochemistry (carboxylation efficiency) and leaf morphol ogy (stomatal density).