Fig 1.
Stomatal aperture response to variations in pCO₂.
Stomatal aperture (SA; n = 800) was measured in plant taxa from different altitudinal origins: high-altitude taxa (“high”; altitude of origin 2,970 m a.s.l.), including Anthyllis vulneraria subsp. valesiaca and Arabis alpina, and low-altitude taxa (“low”; 540 m a.s.l.), including Anthyllis vulneraria subsp. carpatica and Arabidopsis thaliana (Col-0). All plants were cultivated under reduced (30 Pa) and ambient pCO₂ (42 Pa). Marginal means along with their 95% confidence intervals are presented. Statistical analysis results are provided in S3 Table. Different letters denote statistically significant differences at p < 0.05, as determined by post hoc tests.
Table 1.
Marginal effects of environmental factors on stomatal aperture.
Fig 2.
Marginal effects of environmental factors on stomatal aperture.
Effects of (A) partial pressure of CO2 (pCO₂), (B) air temperature, (C) vapor pressure deficit (VPD), and (D) irradiance on stomatal aperture (SA; n = 1’200) of Arabis alpina and Arabidopsis thaliana (Col-0). The data were obtained from four experiments conducted under environmental conditions that varied within the following minimum and maximum ranges: pCO₂ (29.1–51.8 Pa), temperature (18.8–21.6°C), VPD (7.7–13.2 hPa), and irradiance (85 and 175 µmol m ⁻ ² s ⁻ ¹). Marginal means along with their 95% confidence intervals are presented. Statistical analysis results are provided in Table 1.
Fig 3.
Stomatal frequency of plants growing at their natural sites.
(A) Stomatal density (SD; n = 82) and (B) stomatal index (SI; n = 82) were measured in plants growing at their natural sites. High-altitude taxa (“high”; 2,970 m a.s.l., pCO₂ approx. 29 Pa in 2018, the year of sampling) included Anthyllis vulneraria subsp. valesiaca and Arabis alpina, whereas low-altitude taxa (“low”; 540 m a.s.l., pCO₂ approx. 39 Pa) comprised Anthyllis vulneraria subsp. carpatica and Arabidopsis thaliana. Marginal means along with their 95% confidence intervals are presented. Statistical analysis results are provided in S4 Table. Different letters denote statistically significant differences at p < 0.05, as determined by post hoc tests.
Fig 4.
Stomatal frequency of plants from natural sites and their laboratory-grown conspecifics exposed to altitude-specific pCO2 levels.
Stomatal density (SD; A, n = 262; C, n = 239) and stomatal index (SI; B, n = 254; D, n = 239) were measured in plants growing at their natural sites (nat. site) and in those cultivated in growth chambers under altitude-specific pCO₂ conditions. High altitude taxa (Anthyllis vulneraria subsp. valesiaca and Arabis alpina) grew at 2,970 m a.s.l. (pCO₂ approx. 29 Pa) and were cultivated at 30 Pa pCO₂, while the low altitude taxa (Anthyllis vulneraria subsp. carpatica and Arabidopsis thaliana) grew at 540 m a.s.l. (pCO₂ approx. 39 Pa) and were cultivated at 42 Pa pCO₂. Note: A. thaliana cultivated in the growth chambers at 42 Pa is the Col-0 wild-type. Marginal means along with their 95% confidence intervals are presented. The results of the statistical analysis are listed in S5 Table. Different letters denote statistically significant differences at p < 0.05, as determined by post hoc tests.
Fig 5.
Stomatal frequency (SF) response to variations in pCO₂.
Stomatal density (SD; A, n = 836) and stomatal index (SI; B, n = 828) were determined for high-altitude taxa (“high”; altitude of origin 2’970 m a.s.l.), i.e., Anthyllis vulneraria subsp. valesiaca and Arabis alpina, and for low-altitude taxa (“low”; 540 m a.s.l.), i.e., Anthyllis vulneraria subsp. carpatica and Arabidopsis thaliana (Col-0). All plants were cultivated under reduced (30 Pa) and ambient pCO₂ (42 Pa). Marginal means along with their 95% confidence intervals are presented. Statistical analysis results are provided in S6 Table. Different letters denote statistically significant differences at p < 0.05, as determined by post hoc tests.
Fig 6.
Response of above-ground fresh weight to variations in pCO2.
Fresh weight of the above-ground plant parts (n = 194) was measured in high-altitude taxa (“high”; altitude of origin 2’970 m a.s.l.), i.e., Anthyllis vulneraria subsp. valesiaca and Arabis alpina, and for low-altitude taxa (“low”; 540 m a.s.l.), i.e., Anthyllis vulneraria subsp. carpatica and Arabidopsis thaliana (Col-0). All plants were cultivated under reduced (30 Pa) and ambient pCO₂ (42 Pa). Marginal means along with their 95% confidence intervals are presented. Statistical analysis results are provided in S8 Table. Different letters denote statistically significant differences at p < 0.05, as determined by post hoc tests.
Table 2.
Marginal effects of environmental factors on stomatal density.
Fig 7.
Marginal effects of environmental factors on stomatal density.
The effects of (A) partial pressure of CO2 (pCO₂), (B) air temperature, (C) vapor pressure deficit (VPD), and (D) irradiance on stomatal density (SD; n = 1’926) were analyzed in Arabis alpina and Arabidopsis thaliana (Col-0). The data were obtained from nine experiments conducted under environmental conditions that varied within the following minimum and maximum ranges: pCO₂ (29.1–43.3 Pa), temperature (16.7–22.5°C), VPD (10.3–13.7 hPa), and irradiance (85 and 175 µmol m ⁻ ² s ⁻ ¹). Marginal means along with their 95% confidence intervals are presented. Statistical analysis results are provided in Table 2.
Table 3.
Marginal effects of environmental factors on stomatal index.
Fig 8.
Marginal effects of environmental factors on stomatal index.
The effects of (A) partial pressure of CO2 (pCO₂), (B) air temperature, (C) vapor pressure deficit (VPD), and (D) irradiance on stomatal index (SI; n = 490) were analyzed in Arabis alpina and Arabidopsis thaliana (Col-0). The data were obtained from six experiments conducted under environmental conditions that varied within the following minimum and maximum ranges: pCO₂ (29.5–43.3 Pa), temperature (19.0–21.3°C), VPD (10.4–13.7 hPa), and irradiance (85 and 175 µmol m ⁻ ² s ⁻ ¹). Marginal means along with their 95% confidence intervals are presented. Statistical analysis results are provided in Table 3.