Ecophysiological responses and adaptation strategies of Suaeda salsa (L.) Pall. to combined flooding and litter addition

Hydrological changes and litter accumulation are critical factors affecting the ecological restoration of coastal saline-alkali wetlands. To elucidate the physiological adaptation mechanisms of the dominant species Suaeda salsa (L.) Pall. to the combined effects of flooding and litter addition, this study established three waterlogging regimes (non-waterlogged, intermittently waterlogged, and continuously waterlogged) and four litter addition treatments (no litter addition, aboveground litter addition only, belowground litter addition only, and a combination of both addition), and systematically examined the response patterns of its growth performance, photosynthetic capacity, and physiological and biochemical traits. The results showed that: (1) Waterlogging significantly suppressed the growth of S. salsa , and the alleviating effects of litter addition strongly depended on the waterlogging regime. Full and belowground litter additions were most effective under continuous waterlogging; belowground addition yielded the greatest benefits under non-waterlogged and intermittent waterlogging; and compensatory growth was observed under intermittent waterlogging without litter. (2) Litter addition mitigated waterlogging-induced damage to the photosynthetic apparatus, driving a shift from passive defense to active optimization, Notably, belowground litter more strongly promoted carboxylation efficiency and light use efficiency. (3) Belowground litter alone enhanced antioxidant enzyme activities and reduced lipid peroxidation, whereas full litter addition maintained cellular homeostasis through osmotic adjustment. (4) Correlation and PCA indicated that flooding condition was the dominant factor, whereas litter component was associated with resource allocation patterns, suggesting coordinated responses among photosynthetic efficiency, biomass accumulation, and antioxidant defense in S. salsa . In summary, flooding conditions primarily determined the physiological responses of S. salsa . Belowground litter addition was associated with higher resource use efficiency and greater antioxidant enzyme activities, and with a larger contribution of non-stomatal limitations to the decline in P n . These patterns suggest that belowground litter may help maintain growth under flooding, but the mechanisms proposed here remain speculative and require further experimental validation. Unlike previous studies that have largely focused on the individual effects of flooding or litter decomposition, this study reveals the interactive regulation of S. salsa ecophysiological processes by flooding regime and litter component, demonstrating that belowground litter plays an essential role in alleviating flooding stress and maintaining plant growth and resource use efficiency. These findings provide a theoretical basis for promoting the conservation and restoration of S. salsa populations through litter management in coastal saline wetlands, and also offer a reference for the rehabilitation of similarly degraded wetland ecosystems.