Enterolobium contortisiliquum is a neotropical widespread species that occurs in native Atlantic Forest, Cerrado and Caatinga vegetation in Brazil. Outside Brazil, it occurs in Argentina, Bolivia, Paraguay, and Uruguay. The objective of this study was to investigate the influence of high carbon dioxide concentration [CO 2 ] on leaf gas exchange, chlorophyll content, chlorophyll a fluorescence, growth, and biomass allocation among roots, stems, and leaves in young plants of E. contortisiliquum. After germination, twenty days old individuals of E. contortisiliquum were grown in open-top chambers (OTC) at two different [CO 2 ] (400 ppm and 700 ppm). Physiological measurements were made when the plants had been grown in OTC for 170, 200, 230, and 260 days. The higher [CO 2 ] favored the early growth of E. contortisiliquum by increasing maximum net photosynthesis (P N) and water use efficiency. Under high [CO 2 ], root dry mass increased in E. contortisiliquum, which might be a trait that will benefit this species by enhancing water uptake, particularly in seasonally dry environments.