PS 15-193 - Future of coffee: heatwave and drought responses of Coffea arabica and Coffea canephora

Abstract: Caffeinating people around the world, coffee is one of the most socially and economically significant plants globally. Although a diverse genus, two species of Coffea together comprise 99% of coffee consumed: Coffea arabica and Coffea canephora. Coffee production is projected to be negatively impacted under further climate change, including higher temperatures and more frequent and intense droughts. These abiotic stressors are reducing yields and causing a loss of coffee quality. Coffee, like many domesticated crops, has been historically bred for growth and production instead of combined heat and drought stress resilience. To move towards climate-resilient coffee, we must identify physiological and anatomical characteristics associated with coffee response to compound heat and drought stress. We aim to compare the leaf anatomy of Coffea arabica var. 'Typica' and Coffea canephora var. 'Conilion' within the context of water use and climate resilience to identify physiological traits and thresholds important to understanding production and survival in extreme climate stress.

To assess climate stress responses, we compared the physiological ecology of C. arabica and C. canephora by taking measurements of optimal temperature for carbon assimilation (A opt), water use efficiency (WUE opt), and stomatal conductance (gs) across a temperature gradient. We also measured physiological traits such as drought limits (turgor loss point) and thermal tolerance traits.

Plants were established in a controlled-environment chamber with 12-hour photoperiods, and an air temperature of 26°C. We evaluated baseline anatomical characteristics such as leaf thickness and leaf area. An epidermal peel was sampled from leaves of each plant and imaged on a trinocular microscope. We analyzed stomatal peel images using ImageJ to determine stomata aperture area, total length, and total area, as well as epidermal cell area. We observed that C. canephora had a higher stomatal conductance than C. arabica, likely due to the observed difference in anatomical stomatal traits. and will be better for breeding. Stomatal length and area were significantly higher in C. arabica than in C. canephora. Our data suggests that C. canephora may have a more conservative water use strategy. In our ongoing project, we will next expose the plants to an extreme heatwave atop drought, re-measuring physiological and anatomical traits on surviving plants to investigate the potential for acclimation. Coffee production and survival under further climate stress will rely upon plants with combinations of physiological and anatomical traits conferring resilience to these increasingly frequent compound stress events.