Divergent strategies to reduce stomatal pore index during water deficit in perennial angiosperms

Modulation of stomatal development may be an acclimation response to low water availability. However, stomatal development plasticity has been assessed in very few species. We quantified leaf anatomy traits, including stomatal index (SI), density (SD), size (SS), and pore index (SPI), in response to water-deficit stress in river birch (Betula nigra L.), eastern redbud (Cercis canadensis L.), and silver maple (Acer saccharinum L.). Birch and redbud, but not maple, had reduced SPI in response to water deficit. The mechanism by which SPI reduction occurred (via SD or SS) varied among species and with severity of water stress. Despite reduced SPI in birch and redbud, anatomical changes were relatively small and had a minor to no effect on the theoretical maximum stomatal conductance. Furthermore, gas-exchange rates were equivalent to well-watered plants following media re-irrigation. In some tree species, stomatal development is downregulated in response to water deficit conditions. Stomatal development plasticity is facilitated by smaller or fewer stomata, depending upon the species and the intensity of the stress. Water-deficit-induced plasticity in stomatal development is species-specific, likely due to species adaptation to ecological niches.