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

Abstract

In this study, the response of 6-month-old cocoa (Theobroma cacao L.) seedlings to elevated CO2 concentration [ECO2], 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 CO2), [ECO2] 550 ppm, [ECO2] 700 ppm, ET 3 ?C above chamber control, and ET 3 ?C + [ECO2] 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 CO2 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 (Tmax), around 39 ?C in ET treatment against 36 ?C in chamber control, is quite severe on Pn, leaf ?, and biomass accumulation. Similarly, water deficit at 50% FC resulted in the leaf ? reducing to ??14.06 bars at which Pn, leaf area, and biomass were significantly reduced. [ECO2] could ameliorate the negative effect of high temperature and water deficit stress to certain extent. However, the relative response of cocoa seedlings to [ECO2] in improving Pn, leaf ?, biomass, and WUE was greater under 50% FC compared to plants at 100% FC suggested additional advantage of [ECO2] to cocoa under water limited conditions.