Differential Physiological and Biochemical Responses in Oil Palm Seedlings Exposed to Single and Combined Flooding–Salinity Stress

Abstract

Increases in temperature, rainfall, and sea level associated with climate change have intensified flooding and saltwater intrusion, thereby posing a growing threat to oil palm cultivation. To evaluate the effects of these environmental stressors, 12-month-old oil palm seedlings were subjected to control, flooding, salinity, and combined flooding and salinity treatments. Physiological and biochemical parameters were measured, including total chlorophyll, antioxidant enzyme activities, lipid peroxidation, and proline content. Phytochemical profiles, such as total phenolics, flavonoids, alkaloids, terpenoids, and antioxidant activity, were also assessed. Combined stress caused the most severe reductions in chlorophyll and phytochemicals, with increased lipid peroxidation and visible symptoms such as leaf yellowing and adventitious root formation. Proline accumulation was markedly higher under combined stress, suggesting a protective role. In contrast, individual stress treatments induced antioxidant enzyme activity, contributing to reactive oxygen species mitigation. These findings highlight the distinct and synergistic impacts of flooding and salinity on oil palm seedling health. The results offer a foundation for identifying stress-resilient traits, which can support future breeding or management strategies to sustain oil palm productivity under changing climate conditions.