CO₂ enrichment affects eco-physiological growth of maize and alfalfa under different water stress regimes in the UAE

Water stress has been reported to alter morphology and physiology of plants affecting chlorophyll content, stomatal size and density. In this study, drought stress mitigating effects of CO₂ enrichment was assessed in greenhouse conditions in the hot climate of UAE. Commercially purchased maize (Zea mays L.) and alfalfa (Medicago sativa L.) were seeded in three different custom-built cage structures, inside a greenhouse. One cage was kept at 1000 ppm CO₂, the second at 700 ppm CO₂, and the third at ambient greenhouse CO₂ environment (i.e. 435 ppm). Three water stress treatments HWS (200 ml per week), MWS (400 ml per week), and CWS (600 ml per week) were given to each cage so that five maize pots and five alfalfa pots in each cage received same water stress treatments. In maize, total chlorophyll content was similar or higher in water stress treatments compared to control for all CO₂ concentrations. Stomatal lengths were higher in enriched CO₂ environments under water stress. At 700 ppm CO₂, stomatal widths decreased as water stress increased from MWS to HWS. At both enriched CO₂ environments, stomatal densities decreased compared to ambient CO₂ environment. In alfalfa, there was no significant increase in total chlorophyll content under enriched CO₂ environments, even though a slight increase was noticed.