Anaerobic and Antioxidant Activity in Annual Bluegrass (Poa annua) Following Ice Encasement Stress

Ice encasement of annual bluegrass (Poa annua) putting greens can result in hypoxic or anoxic conditions. Organ-specific and direct physiological evidence on the role of anaerobic metabolism and stress responses in annual bluegrass is needed to justify the importance of costly management strategies to reduce hypoxia. A two-year controlled environment study (2022/2023–2023/2024) was conducted in East Lansing, Michigan, to investigate the impact of different durations of ice encasement stress (0, 40 and 60 days) on select reactive oxygen species (ROS), anaerobic metabolites, antioxidant enzyme activity and anaerobic enzyme activity in annual bluegrass. Ice encasement stress significantly influenced anaerobic metabolism and antioxidant responses in annual bluegrass. The content of reactive oxygen species (ROS), including superoxide anion (O₂⁻) and hydrogen peroxide (H₂O₂), increased with prolonged ice encasement, with O₂⁻ increasing 3.43-fold and H₂O₂ increasing 3.42-fold after 60 days of ice encasement. Antioxidant enzyme activities, such as ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD), were upregulated in response to stress caused by prolonged ice encasement. Additionally, anaerobic respiration byproducts increased, with ethanol increasing 12.80-fold, acetaldehyde 4.11-fold and lactic acid 1.41-fold after 60 days of ice encasement. Key metabolic enzymes, including pyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH), also increased with ice encasement duration. Ice encasement had no significant effect on pigment content or fatty acid composition, though organ-specific differences were observed, with roots having higher saturated fatty acids and leaves showing greater unsaturation. Therefore, we conclude that prolonged ice encasement induces anaerobic metabolism and oxidative stress in annual bluegrass, with limited antioxidant activity in crown and root tissues contributing to winterkill susceptibility. Future research should focus on determining ethanol and gas accumulation thresholds, as well as exploring management strategies to enhance antioxidant defences and mitigate hypoxic stress during overwintering.