Paper Reviewed
Martins, M.Q., Rodrigues, W.P., Fortunato, A.S., Leitao, A.E., Rodrigues, A.P., Pais, I.P., Martins, L.D., Silva, M.J., Reboredo, F.H., Partelli, F.L., Campostrini, E., Tomaz, M.A., Scotti-Campos, P., Ribeiro-Barros, A.I., Lidon, F.J.C., DaMatta, F.M. and Ramalho, J.C. 2016. Protective response mechanisms to heat stress in interaction with high [CO2] conditions in Coffea spp. Frontiers in Plant Science 7: 10.3389/fpls.2016.00947.

Noting that certain modelling studies have predicted that coffee plants will be endangered by future global warming, Martins et al. (2016) set about to see if this prediction had any merit. Working with Coffea arabica (cv. Icatu and IPR108) and Coffea canephora (cv. Conilon CL 153), they thus grew coffee plants at 25/20°C (day/night conditions) under either 380 or 700 ppm CO2 concentrations, after which they gradually raised day/night air temperatures to 31/25, 37/30 and 42/34°C. And what did they thereby learn?

Although a day/night tolerance limit of 42/34°C was observed in all three of the coffee varieties they studied, the seventeen scientists report that (1) relevant heat tolerance up to 37/30°C for both CO2 levels was observed, which was (2) "likely supported by the maintenance or increase of [i] the pools of several protective molecules (neoxanthin, lutein, carotenes, &-tocopherol, HSP70, raffinose), [ii] activities of antioxidant enzymes, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase, GR), catalase (CAT), and the upregulated expression of some genes (ELIP, Chaperonin 20)." Among the several findings reported by the seventeen scientists, it was determined that "tolerance to heat stress was compromised at 42/34°C at normal [CO2], whereas at elevated [CO2] a mitigating effect against heat impacts was evident." This mitigating effect, was accomplished "through higher photosynthetic functioning, upregulation of protective molecules, as well as through higher activity of some antioxidant enzymes," which "high [CO2]-dependent effects on antioxidant defenses likely favored the maintenance of reactive oxygen species at controlled levels and would in turn justify the lower heat impact on the photosynthetic components under elevated [CO2]."

In light of these several findings, one can readily see that atmospheric CO2 enrichment does indeed help a variety of coffee plants to tolerate a sizeable upswing in temperature. And so it is that Martins et al. conclude their paper on the subject by stating that their findings "extend our understanding" of how "high [CO2] constitutes a key player [in regard] to coffee heat resilience and acclimation," which is an especially significant finding in light of "predicted future global warming scenarios for coffee crop sustainability."