## 3 Materials and Methods
### Analytical Methods  
For REE analyses, the prepared samples were first dried at 70 \({}^{\circ}\)C, and then both the dried soil, regolith and fresh bedrock were crushed, pulverized by an agate mortar and sieved through a 200 mesh into powder. The powder was baked at 105 \({}^{\circ}\)C to remove adsorbed water before analysis. REEs were measured using inductively coupled plasma-mass spectrometry (ICP-MS). For soil samples, approximately 50 mg of soil sample was digested with 0.5 mL HNO\({}_{3}\) and 1 mL HF in screw-top, PTFE-lined stainless steel bombs at 185 \({}^{\circ}\)C for 24 h. The inner Teflon was removed from the hot plate after cooling, and the solution was evaporated to dryness. The solution was then drained and evaporated to dryness with 0.5 mL HNO\({}_{3}\). This procedure was repeated twice. The final residue was redissolved by adding 1.5 mL HNO\({}_{3}\) and 1.5 mL deionized water. Subsequently, the bomb was resealed and heated at 130 \({}^{\circ}\)C for 3 h. After cooling to room temperature, the final solution was diluted to 50 mL by adding distilled deionized water. For regolith and bedrock samples, approximately 50 mg of powdered samples was digested with 100 mL APS, which was followed by mechanical shaking for 2 h and standing for 30 min. After filtration at medium speed, 2 mL of filterable solution was diluted to 100 mL by adding distilled deionized water. Subsequently, 10 mL of the solution was diluted to 100 mL by adding 1 mL indium (In) solution, 1 mL HNO\({}_{3}\) and deionized water. The _Settellaria bonicalensis_ samples were washed with tap water and deionized water successively and then oven-dried at 75 \({}^{\circ}\)C until the dry weight reached a constant value. Due to the dominant distributions of flavonoid compounds in roots, roots were used for an REE and flavonoid compound test. The dry root samples were ground to a fine powder. Approximately 200 mg of powdered sample was digested with 5 mL HNO\({}_{3}\) in a high-pressure digestion tank for 1 h, which was followed by cooling and removing HNO\({}_{3}\) at 140 \({}^{\circ}\)C. After cooling to room temperature, the solution was diluted to 10 mL by adding deionized water. The reagent blanks of soil, regolith, bedrock, and roots were treated following the same procedures as the corresponding samples. The total analytical errors for REEs in this study were within \(\pm\)6.  
High-Performance Liquid Chromatography (HPLC-DAD) was applied to test the six flavonoid compounds, including bialcin, oroxylin A glycoside, wogonoside, bialclein, wogonin, and oroxylin A. First, the reference substances of the six flavonoid compounds were dissolved in chromatographic methanol and shaken to prepare the reference solution. Second, root powder samples were placed in a volumetric flask with 70% ethanol and shaken. The supernatant was extracted for filtration through a 0.22 \(\upmu\)m filter membrane after ultrasonic extraction for 40 min and cooling to room temperature. Finally, a high-performance liquid chromatograph Water E2695 was utilized to test the flavonoid compounds of the reference solutions and our specimens. Methanol-0.1% phosphoric acid solution was applied to gradient elute the mobile phase. The accuracy was controlled by adding 10% of blank samples and parallel samples during testing according to the specification requirement.