## 5 Discussions
### Relationships between REE and Effective Constituents of Scutellaria baiaclensis  
Flavonoid compounds are effective constituents and secondary metabolites of _Scutellaria baiaclensis_, which are controlled by the growing conditions, including illumination, temperature, moisture, and nutrients [91]. In our study area, flavonoid compounds were more abundant in NGHs than APHs and BCHs. Previous data have demonstrated that mineral nutrient elements (e.g., REE\({}^{3+}\)) control the synthesis and accumulation of flavonoid compounds, either as catalysts for secondary compound metabolism [92; 93; 94; 95; 96], by involving in their functional structure [97; 98; 99; 100] or by contributing to the growth of cells [101; 102; 103; 104; 105]. Pearson correlation analysis was applied to check out further the correlations between micronutrient elements with flavonoid compounds in the roots. The results exhibited that micronutrient elements, including REEs, Cu, Zn, Sr, Ge, and Se, had a significant positive  
Figure 8: Scatter diagram of (**a**) \(\Sigma\)REE in the rhizosphere soils versus roots and (**b**) \(\Sigma\)LREE in the rhizosphere soils versus roots. **_p_ < 0.01. Figure 9: BACs distribution patterns of REEs in roots of _Scutellaria bicalensis_. (**a**) NGHs; (**b**) APHs; (**c**) BCHs. correlation with flavonoid compounds to some extent (\(p<0.05\) or \(p<0.01\)) (Figure 10), indicating that the micronutrient elements of roots have a significant influence on the medicinal composition of _Scutellaria baiaclensis_. It was widely acknowledged that the activation of endocytosis is the primary response of plant cells to REEs [10, 106, 107, 108], which induces a series of physiological and biochemical responses, affecting the activation of various enzymes, substance synthesis and cell growth [104, 107, 109, 110]. Previous studies have demonstrated that exposure to REEs can affect the absorption of mineral elements by plants [111, 112]. In our study area, roots of _Scutellaria baiaclensis_ in NGHs contained higher micronutrient elements concentrations than BCHs and APHs, e.g., Cu, Zn, Sr, Ge and Se (Table 5). Therefore, high REEs and micronutrient elements concentrations of hornblende-gneiss favored the synthesis and accumulation of flavonoid compounds in Scutellaria baiaclensis after the activation of endocytosis induced by REEs [100, 113]. In addition, trivalent lanthanum (La(III)) is similar to Ca\({}^{2+}\) in terms of properties and structures as mentioned above. Therefore, La(III) may substitute for Ca\({}^{2+}\) and present similar effects as Ca\({}^{2+}\) in biological systems [105, 114, 115]. For instance, La(III) may bind to Ca-binding sites in the CaM molecule by electrostatic attraction or coordination [106, 116] based on the concentrations of REEs. Hence, the CAM expression level in plants and its molecular structure was therefore affected by REE concentrations, affecting the accumulation of effective constituents [117]. As mentioned above, we can conclude that parent materials significantly impact the quality of Scutellaria baiaclensis in terms of micronutrient elements involving REEs. Some strategies for management of the habitats of _Scutellaria baiaclensis_ are as follows:  
Figure 10: Pearson correlation analysis between flavonoid compounds and micronutrient elements in the roots of _Scutellaria baiaclensis_.