Summary Carbon assimilation by Cedrela odorata L. (Mel-

iaceae) seedlings was investigated in ambient and elevated CO2 concentrations ([CO2]) for 119 days, using small fumiga-tion chambers. A solution containing macro- and micronutri-ents was supplied at two rates. The 5 % rate (high rate) was de-signed to avoid nutrient limitation and allow a maximum rate of growth. The 1 % rate (low rate) allowed examination of the effect of the nutrient limitation–elevated CO2 interaction on carbon assimilation. Root growth was stimulated by 23 % in el-evated [CO2] at a high rate of nutrient supply, but this did not lead to a change in the root:shoot ratio. Total biomass did not change at either rate of nutrient supply, despite an increase in relative growth rate at the low nutrient supply rate. Net assimi-lation rates and relative growth rates were stimulated by the high rate of nutrient addition, irrespective of [CO2]. We used a biochemical model of photosynthesis to investigate assimila-tion at the leaf level. Maximum rate of electron transport (Jmax) and maximum velocity of carboxylation (Vcmax) did not differ significantly with CO2 treatment, but showed a substantial re-duction at the low rate of nutrient supply. Across both CO2 treatments, mean Jmax for seedlings grown at a high rate of nu-trient supply was 75 µmol m–2 s–1 and mean Vcmax was 27 µmol m–2 s–1. The corresponding mean values for seedlings grown at a low rate of nutrient supply were 36 µmol m–2 s–1 and 15 µmol m–2 s–1, respectively. Concentrations of leaf nitrogen, on a mass basis, were significantly decreased by the low nutrient supply rate, in proportion to the observed decrease in photo-synthetic parameters. Chlorophyll and carbohydrate concen-trations of leaves were unaffected by growth [CO2]. Because there was no net increase in growth in response to elevated [CO2], despite increased assimilation of carbon at the leaf level, we hypothesize that the rate of respiration of non-photo-synthetic organs was increased