Plant treatment
The plants used for the cadmium stress experiments were grown in the greenhouse of Shandong University, Qingdao, China (36°23′10′′ N, 120°36′44′′ E). The greenhouse equipped with glass ceilings receives natural light, with light intensity similar with natural conditions and a photoperiod of 12-14 hours of daylight from May to October. The average daily temperature was maintained at 30.2℃ and the air humidity around 85% by ventilating fans. The same greenhouse settings were maintained throughout the experimental period to guarantee controlled and constant growth conditions. First of all, rhizomes of two genotypes Heze and Panjin of P. australis were collected from the common garden in May, 2022. After one week in the water, the rhizomes were cut into pieces of similar lengths with buds and placed in the pots. Each rhizome piece was planted in a pot with mixed vermiculite and nutrient soil (in a volumn ratio of 2:1) as the substrate. The pots had a top diameter of 16.0 cm, a bottom diameter of 13.0 cm, and a height of 17.5 cm. The water saturated soil weight was about 1.25 kg in each pot, and the dry weight was about 0.35 kg. Three clones grown from the rhizomes of the same genotype were used as independent biological replicates (in separate pots) for each treatment. The concentration of the Cd solution was made of 1.61g CdCl2 per liter of water, i.e., 1mg mL-1 Cd. A survey of spatial and temporal distribution of Cd pollution in farmland soil showed that the farmland soil Cd concentrations ranged from 0.012 to 23.33 mg·kg-1 in China, with the geometric mean of 0.473 mg·kg-1 (J. Wang, Wei, & Pan, 2023). According to the control standards of pollutants in sludge for agricultural use in China issued in 2018 (GB4284-2018), the total cadmium content below 3 mg kg-1 can be classified as Class A pollutants, while the total cadmium content below 15 mg kg-1 can be classified as Class B pollutants. Class A sludge products can be used for farmland, gardens, and pasture, whereas Class B sludge products can be used for gardens, pasture, and non-food crop farmland. Therefore, we set three Cd treatment levels in this study: 0mg kg-1(the control, C), 4mg kg-1 (the low Cd treatment, L), and 20mg kg-1(the high Cd treatment, H). After two-month cultivation of the buds, we will treat these plants with CdCl2 solution. After one-month treatment, the fresh leaves of each individual were collected for RNA extraction, and the cultivars were used for functional traits measurement.