2.1 Study site and sampling
This study was conducted in Hoxud County in the Xinjiang Uyghur Autonomous Region of China (91°45′42″E, 40°39′75″N). This region experiences a semi-arid climate with a mean annual temperature of 12.56 °C and a mean annual precipitation of 591 mm. The sampling sites are located in the watershed area of seasonal floods from radiation-contaminated region with 137Cs accumulation. The soil had a salt content above 2% in the surface layer (< 20 cm deep) and a radionuclide level 3­-5 fold that of normal soil. K. schrenkianum was the dominant population of the local habitat. Plant materials and soil samples were collected from four sites with different environmental radioactivity levels during August and September 2017 (Table S1). Five plants (15 m apart) were uprooted from each site. Whole plants were placed in large autoclaved paper envelopes, labelled, transported to laboratory in an icebox, and stored at -80 °C until further process. Five soil samples were collected with shovels from the surface soil (0-20 cm deep) of each site. Soil samples from each site were sieved to remove rocks and plant litter, pooled, packed and labelled in cloth bags, and stored at 4 °C to transport to the laboratory. The geochemical characteristics, such as pH, electrical conductivity (EC), organic matter (OM), total nitrogen (TN), soluble nitrogen (SN), available phosphorus (P), available potassium (K), salt (Sal), chloride ion (Cl), sulfate (Sulf), calcium ion (Ca), magnesium ion (Mg), and sodium ion (Na), were measured in the Institute of Quality Standards & Testing Technology for Agro-Products, Xinjiang Academy of Agricultural Sciences.