Patterns and mechanisms of ecophysiological responses of Phragmites australis

Coastal wetland, as crucial interconnections between terrestrial and marine ecosystems, are extremely sensitive to invasions from non-native species. Chongming Dongtan, as a significant wetland in the Yangtze River Delta, with Phragmites australis as one of the dominant species, is at constant risk of primary and secondary invasion by alien species Spartina alterniflora, especially in the habitats with relatively high soil salinity. However, P. australis populations can survive in different tidal flat habitats in Chongming Dongtan wetland, although their ecological performances tend to be inconsistent, therefore, its survival strategies and the corresponding mechanisms in the tidal flats with different soil salinities need to be elucidated, so as to provide theoretical basis and technical support for the effectively developing P. australis population in Dongtan wetland, resisting the invasion of S. alterniflora, protecting the structure and function of wetland, and restoring the wetland habitat formerly occupied by S. alterniflora. By comparing the variations of functional traits of P. australis at multiple tidal flats (low, middle and high) and their response to the soil physicochemical properties, this study aims to clarify the salt-tolerant survival strategy and the corresponding mechanisms of P. australis. The results showed that the leaf characteristics such as Soil and Plant Analyzer Development (SPAD) value, specific leaf area and leaf thickness demonstrated more robust stability to soil salinity than the average height and dry weight. Furthermore, as salt stress intensified, the activities of Superoxide dismutase (SOD), Catalase (CAT) and peroxisome (POD) in P. australis leaves at low tidal flat exhibited an upward trend than at other tidal flats. To investigate the molecular mechanism behind salt tolerance in Phragmites australis, we conducted transcriptome sequencing on its leaves at four different tidal habitats. Weighted correlation network analysis (WGCNA) screened out three modules closely related to high salt tolerance. Combined with differentially expressed genes (DEG), identifying 105 core genes crucial for high salt tolerance. Our study focused on the molecular mechanism of the degradation in low-tide level areas, identifying 25 core genes by combining WGCNA and DEG. We observed a decrease in the activity of ferroptosis marker gonyautoxin-4 and an increase in the content of Fe3+ in the degenerate group, indicating that ferroptosis may participate in degradation. Furthermore, correlation analysis indicated a possible regulatory network between salt tolerance and ferroptosis. In a short, this study provides new insights into Salt Tolerance Mechanism of P. australis.