Interspecific variability of plant stomatal response to step changes of [CO2]

The kinetics of a stomatal response to sudden increases or decreases of CO2 concentrations ([CO2]) was studied in 13 plant species growing in the field. Plants were well supplied with water. In each plant, gas exchange measurements were made on a fully developed leaf that was first left to achieve steady-state stomatal conductance (gs) at 400 μmol (CO2) mol−1) and then exposed to a step change of [CO2] (to 700 μmol mol−1 in one experiment; and to 700 and back to 400 μmol mol−1 in a second experiment). Porometric data were captured in intervals of 3 s until a new steady state was reached.A comparison of t1/2, the half-time needed to achieve new gs, indicates similar responses of stomata in grasses when compared to herbs. The stomata of C4 plants responded in approximately 5 min, the highest closure rate was detected in Echinochloa crus-galli and Digitaria sanguinalis. Opening rates were similar to closing rates and the response as a whole was rather symmetric. In C3 plants, the full response of stomata was much slower. Analysis revealed differences in absolute rates of gs change between C3 and C4 plants. These differences can be related to the specificities of the type of photosynthetic metabolism. C4 photosynthesis enables plants to reduce gs, which can hasten further changes of diffusivity in response to the environmental signals. A possible coupling of C4 metabolism to the regulation of guard cells also has to be taken into account when explaining the observed results.

► Stomatal opening and closing at step [CO2] change have similar kinetics. ► C4 plant species can be recognized as fast responders to step [CO2] changes. ► Differences in stomatal kinetics of C4 and C3 might have implications in time-averaged stomatal conductance in the environments with fluctuating carbon dioxide concentrations.