Paper Reviewed
Rosa, B.L., Souza, J.P. and Pereira, E.G. 2019. Increased atmospheric CO2 changes the photosynthetic responses of Acrocomia aculeate (Arecaceae) to drought. Acta Botanica Brasilica 33: 486-497.

Noting that "the response of palm species to elevated CO2 remains poorly understood," Rosa et al. designed an experiment to "investigate the influence of increased CO2 on the response of photosynthesis and biomass production under drought in macauba palm plants."

Macauba palm (Acrocomia aculeate) is a drought-resistant species with a distribution throughout the American tropics. For their study they placed three-month-old saplings in open-top chambers at a facility located at the Federal University of Vicosa, Campus Florestal, Minas Gerais, Brazil, whereupon half were subjected to ambient CO2 air (400 ppm) and half to CO2 enriched air (700 ppm). After 320 days, half of the plants in each CO2 treatment were exposed to water stress by withholding irrigation until the net photosynthetic rate approximated zero, at which point the plants were rehydrated to full recovery. This water-withholding and replenishing cycle was repeated a total of three times over the final 74 days of the study.

Long-term exposure of the palm plants to elevated CO2 conditions resulted in key morphological and physiological adjustments, including increased stomatal conductance, increased Rubisco carboxylation, and increased light use efficiency, all of which factors contributed to an upregulation of photosynthesis and an ultimate enhancement of aboveground biomass production. Elevated CO2 also altered the response of macauba palm to drought. In this regard, plants exposed to 700 ppm CO2 exhibited a faster recovery time after rehydration, maintained relative water content during successive water stress cycles, exhibited higher water use efficiencies and were "more capable of recovering from drought due to higher Rubisco carboxylation rate and electron transport rate, which prevented a reduction in total dry mass at the end of the stress period."

Considering all of the above positive findings, Rosa et al. conclude "the effective responses of macauba palm to drought and elevated CO2 reveal that this plant has the potential to adjust to future climate change."