Figure3. Biplot of environmental factors (soil water content and electrical conductivity) with community characteristics and functional trait variables by redundancy analysis (RDA). Hollow black arrows are soil water content and electrical conductivity; solid blue arrows are functional traits of P. australis . Abbreviations: EC, electrical conductivity; SWC, soil water content; H, average height; Nu, number of plants; SPAD, SPAD values; LWC, leaf water content; SLA, specific leaf area; LA, leaf area; LT, leaf thickness; Lpnu, pitch number; Lpih; internode height; and BSD, base stem diameter. Green indicates plant traits including H and Nu; red indicates leaf traits including SPAD, LT, LA, SLA, and LWC; black indicates stem traits including Lpih, Lph, Lpnu, and BSD.
3.4 P. australis adaptability and plasticity
Environmental factors and selected functional traits of P. australis varied greatly (Table 3), indicating the strong phenotypic plasticity and environmental tolerance of P. australis . The coefficient of variation of soil water content was larger than 25%, while the electrical conductivity was up to 87%. The amplitude of soil water content (9.39–36.92%) and electrical conductivity (0.14–13.29 ms/cm) indicated the high tolerance of P. australis to environmental variables in the Yellow River Delta. The coefficients of variation of leaf traits were lower than 20%, except for the leaf area, while the stem traits were higher than 20%.
Table 3. Statistical characteristics of environmental variables and functional traits for P. australis.