Early growth phase and caffeine content response to recent and projected increases in atmospheric carbon dioxide in coffee (Coffea arabica and C. canephora).

While [CO ₂ ] effects on growth and secondary chemistry are well characterized for annual plant species, little is known about perennials. Among perennials, production of Coffea arabica and C. canephora (robusta) have enormous economic importance worldwide. Three Arabica cultivars (Bourbon, Catimor, Typica) and robusta coffee were grown from germination to ca. 12 months at four CO ₂ concentrations: 300, 400, 500 or 600 ppm. There were significant increases in all leaf area and biomass markers in response to [CO ₂ ] with significant [CO ₂ ] by taxa differences beginning at 122-124 days after sowing (DAS). At 366-368 DAS, CO ₂ by cultivar variation in growth and biomass response among Arabica cultivars was not significant; however, significant trends in leaf area, branch number and total above-ground biomass were observed between Arabica and robusta. For caffeine concentration, there were significant differences in [CO ₂ ] response between Arabica and robusta. A reduction in caffeine in coffee leaves and seeds might result in decreased ability against deterrence, and consequently, an increase in pest pressure. We suggest that the interspecific differences observed (robusta vs. Arabica) may be due to differences in ploidy level (2n = 22 vs. 2n = 4x = 44). Differential quantitative and qualitative responses during early growth and development of Arabica and robusta may have already occurred with recent [CO ₂ ] increases, and such differences may be exacerbated, with production and quality consequences, as [CO ₂ ] continues to increase.