Effects of elevated [CO2] on photosynthesis in European forest species: a meta‐analysis of model parameters

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Abstract
The effects of elevated atmospheric CO2 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 [CO2] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light‐saturated photosynthetic rates (Amax), the potential electron transport rate (Jmax), the maximum Rubisco activity (Vcmax) and leaf nitrogen concentration on mass (Nm) and area (Na) bases. Across all experiments, light‐saturated photosynthesis was strongly stimulated by growth in elevated [CO2]. However, significant down‐regulation of photosynthesis was also observed; when measured at the same CO2 concentration, photosynthesis was reduced by 10–20%. The underlying biochemistry of photosynthesis was affected, as shown by a down‐regulation of the parameters Jmax and Vcmax of the order of 10%. This reduction in Jmax and Vcmax was linked to the effects of elevated [CO2] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO2]. Tables of model parameter values for different European forest species are given.