Long-term elevated air [CO2] strengthens photosynthetic functioning and mitigates the impact of supra-optimal temperatures in tropical Coffea arabica and C. canephora species

The tropical coffee crop has been predicted to be threatened by future climate changes and global warming. However, the real biological effects of such changes remain unknown. Therefore, this work aims to link the physiological and biochemical responses of photosynthesis to elevated air [CO2] and temperature in cultivated genotypes of Coffea arabica L. (cv. Icatu and IPR108) and Coffea canephora cv. Conilon CL153. Plants were grown for ca. 10 months at 25/20 degrees C (day/night) and 380 or 700l CO(2)l(-1) and then subjected to temperature increase (0.5 degrees Cday(-1)) to 42/34 degrees C. Leaf impacts related to stomatal traits, gas exchanges, C isotope composition, fluorescence parameters, thylakoid electron transport and enzyme activities were assessed at 25/20, 31/25, 37/30 and 42/34 degrees C. The results showed that (1) both species were remarkably heat tolerant up to 37/30 degrees C, but at 42/34 degrees C a threshold for irreversible nonstomatal deleterious effects was reached. Impairments were greater in C.arabica (especially in Icatu) and under normal [CO2]. Photosystems and thylakoid electron transport were shown to be quite heat tolerant, contrasting to the enzymes related to energy metabolism, including RuBisCO, which were the most sensitive components. (2) Significant stomatal trait modifications were promoted almost exclusively by temperature and were species dependent. Elevated [CO2], (3) strongly mitigated the impact of temperature on both species, particularly at 42/34 degrees C, modifying the response to supra-optimal temperatures, (4) promoted higher water-use efficiency under moderately higher temperature (31/25 degrees C) and (5) did not provoke photosynthetic downregulation. Instead, enhancements in [CO2] strengthened photosynthetic photochemical efficiency, energy use and biochemical functioning at all temperatures. Our novel findings demonstrate a relevant heat resilience of coffee species and that elevated [CO2] remarkably mitigated the impact of heat on coffee physiology, therefore playing a key role in this crop sustainability under future climate change scenarios.