Impaired Stomatal Control Is Associated with Reduced Photosynthetic Physiology in Crop Species Grown at Elevated [CO2]

Matthew Haworth; Dilek Killi; Alessandro Materassi; Antonio Raschi; Mauro Centritto

doi:10.3389/fpls.2016.01568

Impaired Stomatal Control Is Associated with Reduced Photosynthetic Physiology in Crop Species Grown at Elevated [CO₂]

Front Plant Sci. 2016 Oct 25:7:1568. doi: 10.3389/fpls.2016.01568. eCollection 2016.

Authors

Matthew Haworth¹, Dilek Killi², Alessandro Materassi³, Antonio Raschi³, Mauro Centritto¹

Affiliations

¹ National Research Council - Tree and Timber Institute Florence, Italy.
² Department of Agrifood Production and Environmental Sciences, University of Florence Florence, Italy.
³ National Research Council - Institute of Biometeorology Florence, Italy.

Abstract

Physiological control of stomatal conductance (G_s) permits plants to balance CO₂-uptake for photosynthesis (P_N) against water-loss, so optimizing water use efficiency (WUE). An increase in the atmospheric concentration of carbon dioxide ([CO₂]) will result in a stimulation of P_N and reduction of G_s in many plants, enhancing carbon gain while reducing water-loss. It has also been hypothesized that the increase in WUE associated with lower G_s at elevated [CO₂] would reduce the negative impacts of drought on many crops. Despite the large number of CO₂-enrichment studies to date, there is relatively little information regarding the effect of elevated [CO₂] on stomatal control. Five crop species with active physiological stomatal behavior were grown at ambient (400 ppm) and elevated (2000 ppm) [CO₂]. We investigated the relationship between stomatal function, stomatal size, and photosynthetic capacity in the five species, and then assessed the mechanistic effect of elevated [CO₂] on photosynthetic physiology, stomatal sensitivity to [CO₂] and the effectiveness of stomatal closure to darkness. We observed positive relationships between the speed of stomatal response and the maximum rates of P_N and G_s sustained by the plants; indicative of close co-ordination of stomatal behavior and P_N. In contrast to previous studies we did not observe a negative relationship between speed of stomatal response and stomatal size. The sensitivity of stomata to [CO₂] declined with the ribulose-1,5-bisphosphate limited rate of P_N at elevated [CO₂]. The effectiveness of stomatal closure was also impaired at high [CO₂]. Growth at elevated [CO₂] did not affect the performance of photosystem II indicating that high [CO₂] had not induced damage to the photosynthetic physiology, and suggesting that photosynthetic control of G_s is either directly impaired at high [CO₂], sensing/signaling of environmental change is disrupted or elevated [CO₂] causes some physical effect that constrains stomatal opening/closing. This study indicates that while elevated [CO₂] may improve the WUE of crops under normal growth conditions, impaired stomatal control may increase the vulnerability of plants to water deficit and high temperatures.

Keywords: drought; food security; photosynthetic down-regulation; stomatal behavior; stomatal evolution; stomatal sensitivity.