Leaf hydraulic adaptation of C3 and C4 grasses

Alec S. Baird, Samuel H. Taylor, Jessica Pasquet-Kok, Christine Vuong, Yu Zhang, Teera Watcharamongkol, Hervé Cochard, Christine Scoffoni, Erika Edwards, Colin P. Osborne, Lawren Sack
Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland

Grasses are exceptionally productive globally, with C₃ and C₄ species dominating contrasting environments, yet their hydraulic adaptation has remained paradoxical. Combining physiology, anatomy, meta-analysis and modeling, we validate a hypothesized framework for the linkages of gas exchange with leaf hydraulic transport capacity, anatomy and adaptation to aridity across C₃ and C₄ grasses. We demonstrate that diversity in grass leaf water transport capacity depends on outside-xylem pathways, including vein sheath anatomy. The evolution of higher photosynthetic rate among C₃ grasses depends on higher hydraulic capacity. By contrast, in C₄ grasses the photosynthetic advantage associated with their specialized biochemistry depends on high leaf water transport capacity relative to stomatal conductance. We show strong adaptation of hydraulic and photosynthetic mechanisms to the aridity of species’ native ranges. Our results indicate that hydraulic traits are a previously unexposed element of evolutionary and ecological success in C₃ and C₄ grasses and a crucial target for climate forward crop design.