Assessment of photosynthetic efficiency of greater yam and white yam subjected to elevated carbon dioxide

Carbon dioxide concentration is likely to increase by 2–2.5 fold by the end of 21st century from its current level of 400 ppm due to anthropogenic activities mediated climate change. As yam is an important food and nutrition security crop, it is of paramount importance to assess the effect of climate change on the physiological processes especially photosynthetic efficiency to identify the climate-smart varieties to meet the future food demand. The aim of this experiment was to assess the net photosynthetic rate, stomatal conductance, intercellular CO2, transpiration and physiological water use efficiency of seven yam varieties subjected to 400 ppm (ambient), 600, 800 and 1000 ppm (elevated carbon dioxide concentration). All the parameters were found significant at P<0.001. The mean photosynthetic rate increased significantly increased at 400–1000 ppm and no down-regulation was observed. Similar trend was observed in case of intercellular CO2 and physiological water use efficiency (WUEinstantaneous and WUEintrinsic). However, stomatal conductance increased significantly up to 800 and decreased at 1000 ppm. Contrasting results were recorded with regard to transpiration, which steadily decreased at ascending carbon dioxide concentrations. Further, photosynthesis rate had a significant (P<0.001) positive linear correlation with the elevated carbon dioxide (R2 = 0.783) and intercellular CO2 concentration (R2=0.763). White yam and greater yam were found to be responsive to elevated carbon dioxide as photosynthetic rate at 1000 ppm increased up to ∼68% in comparison to 400 ppm.