Atmospheric change, plant water status and the origins of agriculture

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.

Changes in daily transpiration at the leaf scale in C4 species — Changes in daily transpiration at the leaf scale (E_leaf) in the C₄ species (A) *P. miliaceum* and (B) *S. viridis* and the C₃ species (C) *H. spontaneum* and (D) *T. boeoticum*, over a 3-d drying cycle (D1–D3). Plants were grown at pCO₂ of 18 Pa (closed symbols) and 27 Pa (open symbols). Data are means ± s.e. of four replicates. Significance codes are ***P < 0·001, **P < 0·01, and *P < 0·05, n.s = not significant. Values of E_leaf are set to a different scale for the C₃ and C₄ species.

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.