Plant phenotypic adjustments in response to changes in atmospheric pCO ₂ : insights from δ ¹³ C values and stomatal index in C ₃ plant leaves

The commencement of the Industrial Revolution has resulted in an unprecedented increase in the concentration of atmospheric CO₂ (pCO₂). It is, therefore, important to understand how plant communities respond to increased levels of CO₂ levels in the environment. To this end, we examined the effects of spatial variation in pCO₂ on plant physiology using carbon isotope ratios (δ¹³C values) and stomatal index (SI) in C₃ plant leaves along a transect from the central Ganga Plain to the foothills of the Himalayas with industrial and non-industrial zones. Our study shows that the plants adjacent to the industrial areas have much lower δ¹³C values (avg. -31.8 ‰) and absorbed more fossil fuel-derived carbon (ca. 18 %) than those growing in non-industrial areas (-28.3 ‰). We also observed ca. 25 % lower SI values from the industrial area, suggesting that the increase in CO₂ concentration (for a given water budget) led to high photosynthetic rates with low stomatal conductivity. Therefore, a long-term increase in pCO₂ would lead to higher water-use efficiency in C₃ plants, which would allow them to function better in low moisture conditions. We also suggest that the δ¹³C and SI values can be used for mapping carbon sequestration by plants growing in industrialized regions.