Plant phenotypic adjustments in response to changes in atmospheric pCO2: insights from δ13C values and stomatal index in C3 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.