Leaf gas films enhance metabolic responses to submergence in Cynodon dactylon

Riparian plants frequently experience flooding, which imposes oxygen limitation and disrupts carbohydrate metabolism, threatening survival and post-flood recovery. Certain species, including Cynodon dactylon, form leaf gas films-thin layers of air retained on hydrophobic surfaces-that may alleviate stress hypoxia. However, their effects on central carbon metabolism remain poorly understood. Here, we investigated the role of leaf gas films in the submergence tolerance of C. dactylon by integrating physiological measurements, non-structural carbohydrate analysis, and targeted metabolomics. Plants were subjected to complete submergence with or without gas film retention, and growth, stomatal behavior, oxygen availability, carbohydrate consumption, and metabolite profiles were monitored. Gas films formed rapidly upon submergence, enhancing stomatal opening and maintaining higher oxygen partial pressures near the leaf surface. Submerged plants with intact gas films retained more green leaves, exhibited faster stem elongation, and preserved on non-structural carbohydrates in their leaves compared with plants lacking gas films. Metabolomic analyses revealed that gas films sustained flux through the tricarboxylic acid cycle and the pentose phosphate pathway. This supported uracil biosynthesis and aerobic energy metabolism. In contrast, plants without gas films shifted towards fermentative and secondary metabolic pathways. Gas films persisted for approximately seven days, providing a transient but critical window for aerobic metabolism under flooding conditions. These findings demonstrate that leaf gas films function as an early-phase adaptive mechanism, that promotes carbohydrate homeostasis and energy balance during submergence. By sustaining aerobic respiration and growth, gas films likely contribute to individual survival, competitive advantage, and the ecological resilience of riparian communities under fluctuating water levels.