Figure 4. Effect of elevated CO₂ on NPP.

(a) NPP calculated by the model for constant light, temperature and water content. The blue solid line corresponds to a species adapted to Ordovician climate and an atmospheric CO₂ concentration of 24 PAL and the dashed magenta line corresponds to a species adapted to today's climate and CO₂ concentration. (b) NPP of lichens and bryophytes measured in field or laboratory experiments as a function of ambient CO₂. Each line stands for a different study and each dot represents a measurement of NPP at the corresponding CO₂ concentration. NPP is normalized in order to make the CO₂ response comparable between different species. The inset figure in a focuses on the range of ambient CO₂ shown in b.