A novel hypothesis for the role of photosynthetic physiology in shaping macroevolutionary patterns (Plant Physiol)

In the 450 million(ish) years since plants acquired the ability to live on land, they have caused dramatic changes in the concentrations of atmospheric CO₂ and O₂ levels. As an example, due to tremendous increases in photosynthesis, CO₂ levels dropped and O₂ levels rose dramatically in the late Paleozoic (about 300 million years ago), but then these trends were reversed due to increased plate tectonic and volcano activity. These striking atmospheric changes coincide with changes in the dominance of three groups of vascular plants: first the ferns, then gymnosperms during the period of highest CO₂ levels, followed by angiosperms in the time when CO₂ levels declined again. In this Letter, Yiotis and McElwain investigate how these atmospheric changes might have affected the fitness of these three groups of plants, through modelling following measurements made while altering both gas levels. They show that the groups differ in their photosynthetic efficiency (as consequences of mesophyll and stomatal conductance, as well as Rubisco efficiency) at various CO₂ and O₂ levels, which may have contributed to their relative abundance. They also note that rising CO₂ levels today are likely to favor gymnosperms. (Summary by Mary Williams) Plant Physiol. 10.1104/pp.19.00749