Woody species grown under sun and shade present similar stomatal speed

Stomata are small epidermal pores responsible for the strict control of the amount of CO2 that diffuses into the leaves while controlling the amount of water vapor lost to the atmosphere. The time required for the stomatal valve opening and closing is coordinated with an optimized hydraulic supply and strongly responds to the surrounding environment. We demonstrate that intense shading conditions promote high levels of plasticity in the woody species of Podocarpus macrophyllus, Eucalyptus urophylla, and Capsicum chinense, in a series of hydraulic, anatomical, and gas exchange traits-parameters that have been associated with optimized stomatal kinetics. The high levels of plasticity expressed in these species, however, did not translate into alterations in the time to reach 90% of the maximum stomatal conductance (g(s)) changes (t(90)) when plants were exposed to dynamic changes in irradiance. In some cases, the growth light affected the maximum slope of g(s). This approach, however, was demonstrated not to be ideal for assessing stomatal speed in sun- and shade-acclimated plants as this method was largely dependent on maximum g(s). Our findings suggest that stomatal speed, as demonstrated by t(90), has low phenotypic plasticity and is most likely under a stronger genetic regulation than other leaf and stomatal anatomical traits.

Automated summary

Stomata play a crucial role in regulating gas exchange in leaves. In this study, we investigated the response of stomatal kinetics to shading conditions in three woody plant species. While intense shading conditions promoted high levels of plasticity in hydraulic, anatomical, and gas exchange traits, stomatal speed showed low phenotypic plasticity and appeared to be under stronger genetic regulation. Our findings highlight the importance of genetic factors in determining stomatal speed.