© 1998 Heron Publishing—Victoria, Canada
Long-term photosynthetic acclimation to increased atmospheric CO2 concentration in young birch (Betula pendula) trees
A. Rey (1) and P. G. Jarvis (1)
1. Institute of Ecology and Resource Management, Darwin Building, Edinburgh University, Mayfield Road, Edinburgh EH9 3JU, U.K. / Received Institute of Ecology and Resource Management, Darwin Building, Edinburgh University, Mayfield Road, Edinburgh EH9 3JU, U.K.
Summary
To study the long-term response of photosynthesis to elevated atmospheric CO2 concentration in silver birch (Betula pendula Roth.), 18 trees were grown in the field in open-top chambers supplied with 350 or 700 μmol mol–1 CO2 for four consecutive growing seasons. Maximum photosynthetic rates, stomatal conductance and CO2 response curves were measured over the fourth growing season with a portable photosynthesis system. The photosynthesis model
developed by Farquhar et al. (1980) was fitted to the CO2 response curves. Chlorophyll, soluble proteins, total nonstructural carbohydrates, nitrogen and Rubisco activity were determined
monthly. Elevated CO2 concentration stimulated photosynthesis by 33% on average over the fourth growing season. However, comparison of maximum
photosynthetic rates at the same CO2 concentration (350 or 700 μmol mol–1) revealed that the photosynthetic capacity of trees grown in an elevated CO2 concentration was reduced. Analysis of the response curves showed that acclimation to elevated CO2 concentration involved decreases in carboxylation efficiency and RuBP regeneration capacity. No clear evidence for a redistribution
of nitrogen within the leaf was observed. Down-regulation of photosynthesis increased as the growing season progressed and
appeared to be related to the source–sink balance of the trees. Analysis of the main leaf components revealed that the reduction
in photosynthetic capacity was accompanied by an accumulation of starch in leaves (100%), which was probably responsible for
the reduction in Rubisco activity (27%) and to a lesser extent for reductions in other photosynthetic components: chlorophyll
(10%), soluble protein (9%), and N concentrations (12%) expressed on an area basis. Despite a 21% reduction in stomatal conductance
in response to the elevated CO2 treatment, stomatal limitation was significantly less in the elevated, than in the ambient, CO2 treatment. Thus, after four growing seasons exposed to an elevated CO2 concentration in the field, the trees maintained increased photosynthetic rates, although their photosynthetic capacity was
reduced compared with trees grown in ambient CO2.
Keywords:
carbohydrates, carboxylation capacity, chlorophyll, electron transport capacity, elevated CO2, nitrogen, Rubisco activity, soluble proteins, stomatal limitation.
