Figure 4 . Ecological strategies of P. australis under different environmental conditions based on the 96 areas. Abbreviations: SWC, soil water content; EC, electrical conductivity; C: competitor; S: stress tolerator, R: ruderal.
The ecological strategies of P. australis in the Yellow River Delta under different salt and water conditions mainly consisted of stress tolerator/competitor-stress tolerator (S/CS) (57.3%, C: S: R=28.5: 66.7: 4.7), competitor-stress tolerator (CS) (27.1%, C: S: R=36.0: 57.3: 6.7), stress tolerator/ competitor-stress tolerator-ruderal (S/CSR) (11.5%, C: S: R=29.9: 57.8: 12.3), and rarely competitor-stress tolerator/ competitor-stress tolerator-ruderal (CS/CSR) (3.1%) and stress tolerator (S) (1%) (Figure 4). The major strategies consisted of S/CS and CS (84.4%). The three strategies of S/CS-CS-S/CSR formed a S-C tradeoff strategy axis with weak R, indicating the competition and stress tolerance in high-salinity areas of the Yellow River Delta. The R strategy was the minor one in the Yellow River Delta, mainly distributed in the low-salinity areas. There were no obvious different strategies of P. australis under different soil water contents, while the S strategy was dominant in the Yellow River Delta. However, with the decrease of soil salinity and the increase of soil water content, P. australis gradually shifted to the C strategy.
DISCUSSION