Stomatal traits, gas exchange parameters and their relationships across C3 species: implications for plant evolution

The CO2 and water vapor exchange of leaves is regulated by stomata. To date, stomatal traits and gas exchange parameters during plant evolution and domestication remain unclear. Here, we created a database including 337 observations of stomatal traits and gas exchange parameters in C-3 species, ranging from ferns to angiosperms. The results showed that the light-saturated photosynthetic rate (A(sat)) dramatically increased from ferns and gymnosperms to non-crop angiosperms and further increased to crops. The improvement of A(sat) along phylogeny was related to the increments of mesophyll conductance, which was mainly regulated by stomatal anatomy (stomatal traits). In different groups of angiosperms, woody plants had lower A(sat) and stomatal conductance (g(s)) and larger stomatal size (SS) than herbs. A(sat) in deciduous angiosperm trees was significantly higher than that in evergreen angiosperm trees. The stomatal density (SD), stomatal pore index (SPI), A(sat) and g(s) in annual herbs were higher than those in perennial herbs. The improvement of A(sat) and g(s) in crops was mainly related to the increments of SD. Our results suggested that the improvement in photosynthesis of plants during plant evolution and domestication is related to the increase in SD and to the decrease in SS.