Sustained Photosynthetic Performance of Coffea spp. under Long-Term Enhanced [CO2]

Abstract

Coffee is one of the world’s most traded agricultural products. Modeling studies have predicted that climate change will have a strong impact on the suitability of current cultivation areas, but these studies have not anticipated possible mitigating effects of the elevated atmospheric [CO2] because no information exists for the coffee plant. Potted plants from two genotypes of Coffea arabica and one of C. canephora were grown under controlled conditions of irradiance (800 μmol m-2 s-1), RH (75%) and 380 or 700 μL CO2 L-1 for 1 year, without water, nutrient or root development restrictions. In all genotypes, the high [CO2] treatment promoted opposite trends for stomatal density and size, which decreased and increased, respectively. Regardless of the genotype or the growth [CO2], the net rate of CO2 assimilation increased (34-49%) when measured at 700 than at 380 μL CO2 L-1. This result, together with the almost unchanged stomatal conductance, led to an instantaneous water use efficiency increase. The results also showed a reinforcement of photosynthetic (and respiratory) components, namely thylakoid electron transport and the activities of RuBisCo, ribulose 5-phosphate kinase, malate dehydrogenase and pyruvate kinase, what may have contributed to the enhancements in the maximum rates of electron transport, carboxylation and photosynthetic capacity under elevated [CO2], although these responses were genotype dependent. The photosystem II efficiency, energy driven to photochemical events, non-structural carbohydrates, photosynthetic pigment and membrane permeability did not respond to [CO2] supply. Some alterations in total fatty acid content and the unsaturation level of the chloroplast membranes were noted but, apparently, did not affect photosynthetic functioning. Despite some differences among the genotypes, no clear species-dependent responses to elevated [CO2] were observed. Overall, as no apparent sign of photosynthetic down-regulation was found, our data suggest that Coffea spp. plants may successfully cope with high [CO2] under the present experimental conditions.

Coffee growth, pest and yield responses to free-air CO2 enrichment

“…Although the g s values, integrated over the course of the day, could be decreased by elevated [CO 2 ] under winter conditions in Obatã, our daily averaged g s values were clearly unaffected by the treatments when gas exchange is at its maximum during the growing season (Silva et al 2004). Ramalho et al (2013) observed that g s was also unaffected by the high [CO 2 ] treatment. Saldanha et al (2013) were also unable to detect any changes in stomatal index and density and g s in somatic embryogenesis-derived coffee plantlets grown at 360 or 1000 μmol CO 2 mol −1 .…”

“…These results suggest that photosynthetic downregulation is unlikely to have occurred under our experimental conditions. Notably, Ramalho et al (2013) reported compelling evidence demonstrating lack of downregulation in response to elevated [CO 2 ] (700 μmol CO 2 mol −1 ) in three coffee cultivars grown in large pots in growth chambers for 1 year. Taken together, this information suggests that coffee can sustain relatively high photosynthetic rates under a scenario of increasing atmospheric [CO 2 ].…”

“…Therefore, coffee trees have the potential to greatly increase their photosynthetic rates with increasing atmospheric [CO 2 ]. Indeed, Ramalho et al (2013) studied potted coffee plants growing under different [CO 2 ] levels during 1 year and found greater A (ranging from 34 to 49 %) under elevated (700 μmol CO 2 mol −1 ) than under normal (380 μmol CO 2 mol −1 ) [CO 2 ], with no apparent signs of photosynthetic downregulation. Whether this positive effect persists under field conditions and translates into a larger harvestable crop and less water use under free-air CO 2 enrichment (FACE) is still to be determined.…”

Climatic Vulnerability in Robusta Coffee Mitigation and Adaptation

“…Currently, the interest in C. canephora is growing, due to an increasing consumption of instant coffee and blends, to some uncertainty of C. arabica production related to changing climate conditions (BICC, 2014), and because it shows a better ability to tolerate some climatic events when compared to C. arabica (DaMatta and Ramalho, 2006;Ramalho et al, 2013b;Martins et al, 2014). The increased climate tolerance is related to the evolutionary history of the species.…”

“…Those included severe losses of traditional suitable areas (Assad et al, 2004), significant yield reductions (Gay et al, 2006), extinction of wild populations of C. arabica (Davis et al, 2012), and a strong vulnerability in agricultural, social and economic aspects related to this culture (Baca et al, 2014). Still, future studies must consider the possible mitigating effects of the enhanced atmospheric [CO 2 ] on the adverse impacts of elevated temperatures that have begun to be grasped only recently (Ramalho et al, 2013b;Martins et al, 2014). Furthermore, it was reported that some coffee genotypes are particularly able to adapt to harsh environmental constraints, e.g., temperature, irradiance, water and nutrients (Ramalho et al, 1999;DaMatta and Ramalho, 2006;Fortunato et al, 2010;Batista-Santos et al, 2011;Cavatte et al, 2012;Ramalho et al, 2013a;Scotti-Campos et al, 2014), what further emphasis the need to reinforce such biophysical studies.…”