Paper Reviewed
Linkosalo, T., el-Khouri, H., Mäkipää, R., Pulkkinen, P. and Juurola, E. 2017. Increased atmospheric CO2 concentration enhances the development of photosynthetic capacity beyond the temperature effect for silver birch in simulated future climate. Scandinavian Journal of Forest Research 32: 651-657.

Introducing their work, Linkosalo et al. (2017) note that present-day atmospheric CO2 concentrations are a limiting factor for the photosynthetic production of plants, opining that an "increased CO2 concentration [might be expected] to enhance the development of the photosynthetic apparatus of trees during the spring after the leaf flushing, as more carbon is available for the buildup of the photosynthetic apparatus." And, thus, it was their objective to determine if this outcome is indeed the case.

In doing so, the authors grew silver birch trees (Betula pendula) in controlled-environment greenhouses under current and projected future (700 ppm CO2, between only 1000 and 1400 hours and +3°C above ambient the entire day) climate conditions, measuring photosynthetic activity during spring development when leaves sprouted from buds to full photosynthetic production capacity.

The results, in the words of the authors, showed that elevated CO2 had "a direct impact on the rate of development of the photosynthetic potential of [the] photosynthetic apparatus ... beyond the impact of the increased air temperature promoting the development," such that under future atmospheric CO2 concentrations, photosynthetic efficiency should be accelerated and photosynthetic capacity achieved "4-5 days earlier" than it is today.

These findings are well in line with other studies demonstrating the impact of elevated CO2 on enhancing the early spring growth of trees (see, for example, the several studies we have reviewed on this topic here). Furthermore, as noted by Linkosalo et al., they also demonstrate that "when phenological models are used to predict the advancement of the onset of the photosynthetic activity of birch (and probably also other boreal deciduous species), the direct impact of elevated CO2 concentration needs to be taken into account."