Photosynthetic pathway and ecological adaptation explain stomatal trait diversity amongst grasses


Author for correspondence:
C. P. Osborne
Tel: +44 114 222 0146


  • The evolution of C4 photosynthesis in plants has allowed the maintenance of high CO2 assimilation rates despite lower stomatal conductances. This underpins the greater water-use efficiency in C4 species and their tendency to occupy drier, more seasonal environments than their C3 relatives.
  • The basis of interspecific variation in maximum stomatal conductance to water (gmax), as defined by stomatal density and size, was investigated in a common-environment screening experiment. Stomatal traits were measured in 28 species from seven grass lineages, and comparative methods were used to test for predicted effects of C3 and C4 photosynthesis, annual precipitation and habitat wetness on gmax.
  • Novel results were as follows: significant phylogenetic patterns exist in gmax and its determinants, stomatal size and stomatal density; C4 species consistently have lower gmax than their C3 relatives, associated with a shift towards smaller stomata at a given density. A direct relationship between gmax and precipitation was not supported. However, we confirmed associations between C4 photosynthesis and lower precipitation, and showed steeper stomatal size–density relationships and higher gmax in wetter habitats.
  • The observed relationships between stomatal patterning, photosynthetic pathway and habitat provide a clear example of the interplay between anatomical traits, physiological innovation and ecological adaptation in plants.