Abstract
CO2, temperature, water availability and light intensity were potential selective pressures to propel the initial evolution and global expansion of C4 photosynthesis in grasses. To tease apart the primary selective pressures along the evolutionary trajectory, we coupled photosynthesis and hydraulics models and optimized photosynthesis over stomatal resistance and leaf/fine-root allocation. We also examined the importance of nitrogen reallocation from the dark to the light reactions. Our results show that the higher stomatal resistance and leaf/root allocation ratio conferred by the C4 photosynthesis led to C4 advantage without any change in hydraulic conductance. For the initial evolution of C4 25-32 MYA, water limitation was the primary driver, and N reallocation was necessary. Low CO2, together with light intensity, were the primary drivers during the global radiation of C4 5-10 MYA, during this period N reallocation would not have been strongly selected.
Footnotes
Statement of authorship: HZ, BH and EA came up with the idea. HZ and EA built the model, BH put the idea in a general historical context, HZ performed the modeling work and analyzed output data. HZ wrote the first draft, BH and EA contributed substantially to revisions.
Conflict of interest: None declared.