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ABSTRACT The effects of elevated atmospheric CO 2 concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life‐span of a tree. Long‐term, process‐based computer models must be used to extrapolate from shorter‐term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta‐analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field‐based elevated CO 2 experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light‐saturated photosynthetic rates ( A max ), the potential electron transport rate ( J max ), the maximum Rubisco activity ( V cmax ) and leaf nitrogen concentration on mass ( N m ) and area ( N a ) bases. Across all experiments, light‐saturated photosynthesis was strongly stimulated by growth in elevated CO 2 . However, significant down‐regulation of photosynthesis was also observed; when measured at the same CO 2 concentration, photosynthesis was reduced by 10–20%. The underlying biochemistry of photosynthesis was affected, as shown by a down‐regulation of the parameters J max and V cmax of the order of 10%. This reduction in J max and V cmax was linked to the effects of elevated CO 2 on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated CO 2 . Tables of model parameter values for different European forest species are given.
Medlyn et al. (Wed,) studied this question.