Effect of high concentrations of CO2 and high temperatures on the physiology of Mexican cocoa

Climate change affects the physiology of cocoa; however, research under high temperature and elevated [CO2] is scant. It is important to consider the physiological response of cocoa to the interaction of these environmental variables and thus generate an accurate prediction of how this crop will respond to climate change. In order to know whether elevated [CO2] leads to an increase in photosynthetic rate (A) and water use efficiency (WUE), thereby decreasing the negative impact of elevated temperature on physiology of cocoa (Theobroma cacao L), gas exchange, diurnal carbon:water balance (DCWB), photochemical activity of PSII, response curves of A to intercellular [CO2] (A/Ci curves) and growth were determined in two high temperature (T) sensitive cocoa clones (INIFAP-8 and Neocriollo) cultivated in controlled growth chambers for 100 days. The chamber environmental conditions were low [CO2]-low T (LCLT; 400 mu mol CO2 mol-1 and 30 degrees C); high [CO2]-high T (HCHT; 1200 mu mol CO2 mol-1 and 40 degrees C); high [CO2]-low T (HCLT; 1200 mu mol CO2 mol-1 and 30 degrees C) and low [CO2]-high T (LCHT; 400 mu mol CO2 mol-1 and 40 degrees C). A significant increase in A, WUE, DCWB and growth was found in both clones grown at high [CO2]. However, high T (40 degrees C) considerably decreased the physiology of both clones but its impact was significantly mitigated by elevated [CO2]. The results show that the physiological effects generated by elevated [CO2] could reduce the negative impact of increased temperatures, increasing the tolerance range of cocoa in the future.