C₄ photosynthetic anatomy is associated with higher leaf hydraulic conductance and capacitance in Alloteropsis...

The evolution of C₄ photosynthesis requires biochemical innovations to be coordinated with anatomical modifications. In many C₄ species, CO₂ is concentrated and fixed within leaf bundle sheath tissues, which are enlarged relative to other leaf tissues via cell expansion and the insertion of additional minor veins. In this study, we tested the hypothesis that anatomical adaptations for C₄ photosynthetic carbon assimilation also improve plant-water relations. We measured leaf hydraulics and water retention characteristics in photosynthetically diverse populations of the grass Alloteropsis semialata. C₄ individuals of Alloteropsis semialata had higher values of leaf capacitance and leaf hydraulic conductance than non-C₄ plants. Greater minor vein density contributed to higher values of leaf hydraulic conductance and less negative leaf water potential. Moreover, a greater ratio of bundle sheath area : leaf width and thicker leaves were associated with higher values of leaf capacitance and more negative turgor loss points in C₄ plants. Further diversification of leaf water relations traits was related to secondary adaptations to climate and polyploid formation. These findings are consistent with the hypothesis that anatomical adaptations for C₄ photosynthesis also improve plant-water relations in grasses and explain how C₄ photosynthesis expanded the hydrological niche in this species.