Response of Antioxidant Enzymes of Winter Wheat (Triticum aestivum L.) to Shallow and Saline Groundwater Depths

Antioxidant enzymes in plants are critical for protection against oxidative stress and for the overall health and resilience of plant systems. However, antioxidant responses of plants grown in shallow and saline groundwater are poorly understood. Therefore, understanding the biochemical responses of plants to shallow groundwater significantly affects food security and environmental conservation. With this aim, the present work was carried out for 2 years in drainable lysimeters to assess the effects of four different groundwater salinities (0.38, 2.0, 4.0 and 8.0 dS m⁻¹) on the temporal changes in antioxidant enzymatic activity in wheat plants under three different groundwater depths (30, 55 and 80 cm). Superoxide dismutase (SOD), glutathione S-transferase (GST) and catalase (CAT) activities varied significantly based on groundwater depth and salinity. CAT and GST enzyme levels increased curvilinearly with rising groundwater depth and salinity. Conversely, the GR enzyme activity showed no significant change with groundwater depths but increased linearly with higher salinity. SOD enzyme activity notably increased at a groundwater depth of 30 cm but decreased at a depth of 80 cm. Moreover, the peak activity of the GR enzyme was observed at a 6 dS m⁻¹ groundwater salinity under groundwater depths. Additionally, the GST and CAT enzyme activities were inhibited more when the groundwater depth was <55 cm and the groundwater salinity was >4.20 dS m⁻¹. Finally, identifying the peak levels of antioxidant enzymes could potentially serve as an indicator for determining the optimal timing for applying stress mitigation methods in areas with shallow and saline groundwater.