Divergent germination strategies of Phragmites australis seeds for tidal flat gradient adaptation and the implications for coastal wetland restoration

Jing Jia¹Peng Jia²Caifen Yu²Dezhi Li^1*Jiangtao Wang¹Ying Wang¹Jing Chen¹

• ¹East China Normal University, Shanghai, China
• ²National Marine Environmental Monitoring Center, Dalian, Liaoning Province, China

Phragmites australis, capable of both sexual and asexual reproduction, was widely distributed along tidal flat gradients in Chongming Dongtan wetlands, eastern China. To assess maternal effects, seeds from different tidal flat habitats were collected, and the impacts of soil properties, storage temperature, and salinity on germination were examined. At 1.5% salinity, germination rates ranged from 1.3% to 7.7%. When salinity increased to 2.0%, germination rates declined sharply—by 94.3% (L), 96.5% (IN), 100% (M), and 99.2% (H) compared to controls. Higher salinity also slowed germination speed and reduced the germination index.Low-temperature storage (4 °C) significantly enhanced germination rates and potentials, particularly for the low-tidal flat population (L), compared to room temperature (20 °C). Soil salinity and water content were key factors affecting germination after 4 °C storage, while phosphorus levels positively correlated with germination performance. In contrast, room temperature storage more strongly influenced germination speed and index.Structural equation modeling (SEM) explained 74% and 50% of germination variation under 4 °C and room temperature storage, respectively. The tidal level had a stronger direct negative effect on germination at 4 °C (-0.97) than at 20 °C (-0.16). Both storage temperatures and tidal flat origins directly improved germination traits, whereas soil N/P indirectly enhanced germination only at 4 °C.These findings suggest that post-ripening (low-temperature storage) differentially enhances P. australis seed germination across tidal flat gradients in a subtropical salt marsh, demonstrating maternal effect adaptation. Thus, using seeds from natural tidal flat gradients could be an effective and economical approach for population restoration.