Effect of elevated CO2, high temperature, and water deficit on growth, photosynthesis, and whole plant water use efficiency of cocoa (Theobroma cacao L.)

In this study, the response of 6-month-old cocoa ( Theobroma cacao L.) seedlings to elevated CO 2 concentration [ECO 2 ], elevated temperature [ET], and their interaction with water deficit stress was studied in an open top chamber (OTC). Each OTC was maintained at chamber control (400 ppm CO 2 ), [ECO 2 ] 550 ppm, [ECO 2 ] 700 ppm, ET 3 °C above chamber control, and ET 3 °C + [ECO 2 ] 550 ppm. Inside each OTC, a set of plants received moisture at 100% FC, while the other set was at 50% FC, which was the water deficit stress treatment. Increasing the CO 2 concentration in cocoa increased photosynthesis (Pn) by 27%, which resulted in high biomass accumulation, thus improving the whole plant water use efficiency (WUE). The impact of high temperature ( T max ), around 39 °C in ET treatment against 36 °C in chamber control, is quite severe on Pn, leaf Ψ, and biomass accumulation. Similarly, water deficit at 50% FC resulted in the leaf Ψ reducing to − 14.06 bars at which Pn, leaf area, and biomass were significantly reduced. [ECO 2 ] could ameliorate the negative effect of high temperature and water deficit stress to certain extent. However, the relative response of cocoa seedlings to [ECO 2 ] in improving Pn, leaf Ψ, biomass, and WUE was greater under 50% FC compared to plants at 100% FC suggested additional advantage of [ECO 2 ] to cocoa under water limited conditions.