© 2000 Heron Publishing—Victoria, Canada
Interaction of nutrient limitation and elevated CO2 concentration on carbon assimilation of a tropical tree seedling (Cedrela odorata)
F. E. Carswell (1, 2, 3), J. Grace (1, 3), M. E. Lucas (1) and P. G. Jarvis (1)
1. Institute of Ecology and Resource Management, University of Edinburgh, King’s Buildings, Mayfield Road, Edinburgh EH9 3JU,
U.K. / 2. Landcare Research, P.O. Box 69, Lincoln 8152, New Zealand (carswellf@landcare.cri.nz) / 3. Royal Botanic Garden of Edinburgh, Inverleith Row, Edinburgh EH3 5LR, U.K. () / Received September 2, 1999
Summary
Carbon assimilation by Cedrela odorata L. (Meliaceae) seedlings was investigated in ambient and elevated CO2 concentrations ([CO2]) for 119 days, using small fumigation chambers. A solution containing macro- and micronutrients was supplied at two rates.
The 5% rate (high rate) was designed 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 elevated [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 assimilation
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 assimilation 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 reduction at the low rate of nutrient supply. Across both CO2 treatments, mean Jmax for seedlings grown at a high rate of nutrient 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 photosynthetic parameters. Chlorophyll and carbohydrate concentrations 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-photosynthetic
organs was increased.
Keywords:
plant growth, nutrient supply, photosynthetic acclimation, respiration.
