The genesis of agricultural practice marks one of the most important events in human history. Low atmospheric CO2 has previously been shown to limit the productivity of the wild progenitors of C3 and C4 founder crops, in part due to the direct effect of reduced CO2 availability on photosynthesis. In this study, Cunniff et al. investigate the indirect role of low CO2 on biomass limitation mediated via plant water status in cereal crops.
They find that reduced plant water status caused a negative feedback on stomatal aperture in plants at glacial CO2, thereby reducing photosynthesis. These indirect effects were stronger in the C4 species.