Comparative study on the effect of elevated levels of carbon dioxide on growth and photosynthesis of three selected plant species.

The aim of this study was to evaluate the growth and physiological responses of two C3 species (Capsicum annuum and Mentha × piperita) and one C4 species (Gomphrena globosa) under elevated CO2 conditions. Plants were exposed to three CO2 concentrations-~400 parts per million (ppm) (control), ~2,900 ppm, and ~5,400 ppm-in a controlled greenhouse experiment. Elevated CO2 significantly enhanced plant height, leaf number, bud formation, shoot and root fresh weight, total biomass, chlorophyll content, and relative leaf nitrogen index across all species. The magnitude of response differed among species, with C. annuum showing the strongest overall growth stimulation at 5,400 ppm. Multivariate analyses further confirmed that CO2 concentration significantly influenced physiological parameters. These findings demonstrate species-specific responses of C3 and C4 plants to high CO2 enrichment and highlight potential implications for crop productivity under changing atmospheric conditions.