Plant Responses to Very Low Atmospheric CO2 Concentrations
Temme, A.A., Cornwell, W.K., Cornelissen, J.H.C. and Aerts, R. 2013. Meta-analysis reveals profound responses of plant traits to glacial CO2 levels. Ecology and Evolution 3: 4525-4535.
The four Dutch researchers report that "on average across all species," a 50% reduction in current atmospheric CO2 reduced net photosynthesis by 38%, intrinsic water use efficiency by 48% and total plant dry biomass by 47%. Thus, Temme et al. conclude that in terms of carbon gain and whole-plant growth rate, responses to low CO2 are, in fact, somewhat more extreme than responses to high CO2, the latter of which gradually diminish in magnitude as the air's CO2 concentration rises higher and higher.