Elevated [CO₂] benefits coffee growth and photosynthetic performance regardless of light availability

Despite being evolved in shaded environments, most coffee (Coffea arabica L.) is cultivated worldwide under sparse shade or at full sunlight. Coffee is ranked as greatly responsive to climate change (CC), and shading has been considered an important management strategy for mitigating the harmful CC outcomes on the crop. However, there is no information on the effects of enhanced [CO₂] (eC_a) on coffee performance in response to light availability. Here, we examined how carbon assimilation and use are affected by eC_a in combination with contrasting light levels. For that, greenhouse-grown plants were submitted to varying light levels (16 or 7.5 mol photons m^-2 day^-1) and [CO₂] (ca. 380 or 740 μmol mol^-1 air) over six months. We demonstrated that both high light and eC_a improved growth and photosynthetic performance, independently. Despite marginal alterations in biomass partitioning, some allometric changes, such as higher root biomass-to-total leaf area and lower leaf area ratio under the combination of eC_a and high light were found. Stimulation of photosynthetic rates by eC_a occurred with no direct effect on stomatal and mesophyll conductances, and no signs of photosynthetic down-regulation were found irrespective of treatments. Particularly at high light, eC_a led to decreases in both photorespiration rates and oxidative pressure. Overall, our novel findings suggest that eC_a could tandemly act with shading to mitigate the harmful CC effects on coffee sustainability.