Changes of photosynthetic capacity of some plant species under very high CO2 concentrations in Biosphere 2

Conclusions The initial slope of A/ light curve became steep under high CO₂ (700 μmol · mol^-1) compared with that under low CO₂ (350 μmol · mol^-1) for the C₃ species growing in very high CO₂(>2 200 μmol · mol^-1) for a long period. The light compensation points remained unchanged, but the light saturation points were found increased. The ϕ_m,_app and A_max of the C₃ species increased respectively by 79 % and 80 %, while those of C₄ species decreased by 10% and 14%, respectively. The shape of A/light curve of C₄ species did not change. Such results indicated that C₃ species increased the capacity of photosynthesis, while C₄ did not change, otherwise it decreased a little. This work only compared the changes of capacity in photosynthesis of some species under different CO₂ levels in Biosphere 2. We need further investigation on the effects of high CO₂ on the same species outside Biosphere 2, in order to fully undertand the effects and mechanism of response of plants to the elevated CO₂.