Evaluation of photosynthetic efficiency of yam bean (Pachyrhizus erosus L.) at saturating photon flux density under elevated carbon dioxide.

The future CO2 concentration is projected to reach 900-1000 ppm levels by the end of twenty-first century, pertaining to global climatic changes. Consequences of climate change such as changes in mean climatic conditions, increasing extreme weather events, relentless increase in atmospheric CO2 concentration and increasing pest damage pose serious threats to agricultural productivity. An experiment was planned to assess the response of yam bean to elevated CO2, as it is of paramount importance to identify photosynthetically efficient climate-smart crops and varieties to meet future food demand. The net photosynthetic rate (P n ), stomatal conductance (g s ) and intercellular CO2 (C i ) of yam bean variety, Rajendra Misrikand-1 was recorded under elevated carbon dioxide (400-1000 ppm) and photon flux density (PPFD; 50-2000 µmol m-2 h-1) at 30 ± 2 °C, 70-80% relative humidity and 0.8-1.2 kPa vapour pressure deficit. The mean P n rate steadily increased at 200-1000 ppm owing to enhanced intercellular CO2. The same trend was observed in the case of intercellular CO2. However, contrasting results were recorded with regard to g s , which steadily decreased at ascending carbon dioxide concentrations. Further, P n had a significant (P < 0.001) linear correlation with the PPFD (R2 = 0.973). Yam bean was found to be responsive to elevated carbon dioxide as P n rate at 1000 ppm increased up to 23% relative to 400 ppm.