Effect of elevated CO2, high temperature, and water deficit on growth, photosynthesis, and whole plant water use efficiency of cocoa (Theobroma cacao L.)
2020
Hebbar, K. B. | Apshara, Elain | Chandran, K. P. | Prasad, P. V Vara
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 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. [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 Ψ, 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.
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