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The aim of this study was to evaluate the effects of elevated CO
2
concentration on acclimation mechanisms related to gas exchange, photochemical activity, photorespiration, and oxidative protection in cashew plants exposed to salinity. Thirty-day-old cashew plants were irrigated with nutrient solution without (control) or with supplemental NaCl (100 mM) for 2 weeks in the greenhouse. Afterward, control and salt-stressed plants were transferred to the growth chamber and supplied with atmospheric (380 µmol mol
−1
) or high CO
2
(760 µmol mol
−1
) concentrations for 15 days. The results show that elevated CO
2
alone reduced the CO
2
net assimilation rate (
P
N
) without affecting stomatal conductance (
g
S
) and transpiration rate (
E
), whereas salinity and NaCl + high CO
2
reduced the
P
N
associated with a decrease in
g
S
and
E
. The potential quantum yield of photosystem II (Fv/Fm) was not altered, but a slight reduction in electron transport rate and photochemical quenching (qP) in response to high CO
2
alone or combined with NaCl occurred. However, non-photochemical quenching increased due to the effects of high CO
2
and NaCl alone and by their combination. High CO
2
alleviated the toxic effects of Na
+
favoring the K
+
/Na
+
ratio under salinity. High CO
2
coupled with salinity decreased glycolate oxidase activity and the contents of hydrogen peroxide (H
2
O
2
), NH
4
+
, and glyoxylate. Furthermore, we observed increase in membrane damage associated with increased thiobarbituric acid-reactive substances levels under high CO
2
. High CO
2
also decreased ascorbate peroxidase activity, but did not affect superoxide dismutase activity. In general, our data suggest that high CO
2
could induce acclimation processes in plants independent of salinity, revealing a set of responses that are more associated with acclimation than with protective responses.