Effects of elevated carbon dioxide on stomatal characteristics and carbon isotope ratio of Arabidopsis thaliana ecotypes originating from an altitudinal gradient

Stomatal functioning regulates the fluxes of CO2 and water vapour between vegetation and atmosphere and thereby influences plant adaptation to their habitats. Stomatal traits are controlled by external environmental and internal cellular signalling. The objective of this work was to quantify the effects of CO2 enrichment (CE) on stomatal density-related properties, guard cell length (GCL) and carbon isotope ratio (δ13C) of a range of Arabidopsis thaliana ecotypes originating from a wide altitudinal range (50–1260 m above sea level (asl)), and grown at 400 and 800 ppm [CO2], and thereby elucidate the possible adaptation and acclimation responses controlling stomatal traits and water use efficiency (WUE). There was highly-significant variation among ecotypes in the magnitude and direction of response of stomatal traits namely, stomatal density (SD) and index (SI) and guard cell length (GCL), and δ13C to CE, which represented a short-term acclimation response. A majority of ecotypes showed increased SD and SI with CE with the response not depending on the altitude of origin. Significant ecotypic variation was shown in all stomatal traits and δ13C at each [CO2]. At 400 ppm, means of SD, SI and GCL for broad altitudinal ranges, i.e. low (400 m), increased with increasing altitude, which represented an adaptation response to decreased availability of CO2 with altitude. δ13C was negatively correlated to SD and SI at 800 ppm but not at 400 ppm. Our results highlight the diversity in the response of key stomatal characters to CE and altitude within the germplasm of A. thaliana and the need to consider this diversity when using A. thaliana as a model plant