Differential drought tolerance in two commercial açaí cultivars: Insights from gas exchange, chlorophyll fluorescence, and antioxidant responses

The effects of water deficit on leaf gas exchange, chlorophyll fluorescence, and antioxidant enzyme activity were evaluated in two açaí cultivars (BRS-PA and BRS-PD) to assess potential differences in drought tolerance. Plants were compared under full irrigation (Control) and under water deficit marked by predawn leaf water potential around – 2.3 MPa. In both cultivars, drought caused similar decreases in net CO₂ assimilation rate (A), stomatal conductance, Rubisco instantaneous carboxylation efficiency, and transpiration, accompanied by increases in substomatal CO₂ concentration and instantaneous water-use efficiency. In both cultivars, maximum photochemical efficiency of PSII remained unaffected, but actual quantum yield and photochemical quenching declined under stress. The ratio between electron transport rate and A increased by 219% in BRS-PA and 130% in BRS-PD. Chlorophyll a and b, and carotenoids were more strongly reduced in BRS-PD. Superoxide dismutase increased in both cultivars, while ascorbate peroxidase remained unchanged. Catalase activity declined by 40% only in BRS-PD. Lipid peroxidation rose by around 280% in both cultivars, but foliar H₂O₂ accumulation was greater in BRS-PA (37%) than in BRS-PD (21%). Therefore, under the imposed water deficit conditions, cultivars BRS-PA and BRS-PD exhibited comparable overall physiological performance, however, BRS-PD displayed subtle advantages in photoprotective and antioxidant adjustments, potentially conferring greater resilience to prolonged or severe drought than BRS-PA.