Abstract: To explore the adaptive strategies of the clonal plant Phragmites australis in heterogeneous salt habitats, we conducted a pot control experiment with severing, salt heterogeneity and competition treatment using dominant plants from the Yellow River Delta, including P. australis and Suaeda salsa. This study assessed the effects of salt heterogeneity, clonal integration and interspecific competition on the morphological and physiological traits of P. australis. The results showed that clonal integration significantly promoted root system growth and underground biomass accumulation of P. australis. Competition significantly reduced plant height, tiller number, leaf number, leaf length and internode length, inhibiting above- and underground biomass accumulation. Under the heterogeneous salt treatment, clonal integration significantly promoted only the rhizome biomass of P. australis. The S. salsa competition treatment significantly lowered the chlorophyll contents, net photosynthetic rate, stomatal conductance and transpiration rate of P. australis. Nevertheless, leaf length and width were maintained, potentially to minimize photoinhibition. Competition significantly reduced K⁺ contents in P. australis fine roots and rhizomes and Na⁺ contents in fine roots. The Na⁺ content of fine roots was significantly affected by competition, salt heterogeneity, severing treatment and the interaction between competition and severing treatment. In conclusion, competition significantly inhibited the growth, photosynthesis and ion content accumulation of P. australis. Meanwhile, clonal integration promoted root growth, especially under heterogeneous salt conditions. Hence, this research provided a significant and deeper understanding of the ecological adaptive responses of clonal plants in coastal heterogeneous habitats.

Key words: ecological adaptation, interspecifc competition, Phragmites australis, salt heterogeneity, the Yellow River Delta