Impaired Stomatal Control Is Associated with Reduced Photosynthetic Physiology in Crop Species Grown at Elevated [CO2].
Physiological control of stomatal conductance (Gs) permits plants to balance CO2-uptake for photosynthesis (PN) against water-loss, so optimizing water use efficiency (WUE). An increase in the atmospheric concentration of carbon dioxide ([CO2]) will result in a stimulation ofPNand reduction ofGsin many plants, enhancing carbon gain while reducing water-loss. It has also been hypothesized that the increase in WUE associated with lowerGsat 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 ofPNandGssustained by the plants; indicative of close co-ordination of stomatal behavior andPN. 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 ofPNat 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 ofGsis 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.
National Research Council - Tree and Timber Institute Florence, Italy.
Matthew
M
Haworth
Department of Agrifood Production and Environmental Sciences, University of Florence Florence, Italy.
Dilek
D
Killi
National Research Council - Institute of Biometeorology Florence, Italy.
Alessandro
A
Materassi
National Research Council - Institute of Biometeorology Florence, Italy.
Antonio
A
Raschi
National Research Council - Tree and Timber Institute Florence, Italy.
Mauro
M
Centritto
drought; food security; photosynthetic down-regulation; stomatal behavior; stomatal evolution; stomatal sensitivity