## 3 Results and Discussion
### Factors Affecting the Total Amount of Selenium (Se) in Soil and the Various Forms of Se  
Regarding the correlation analysis between the total amounts of Se in the soil and \(G\). _elata_ (Figure 3) samples, a weak correlation was observed (R = 0.32), indicating that the mechanism of plant Se absorption in the soil is complex and that the Se content of plants does not solely depend on the total amount of Se in the soil. As shown in Table 3 and Figure 3, the Se content of \(G\). _elata_ exhibited significant positive correlations with the contents of water-soluble (R = 0.68), exchangeable Se (R = 0.62), and OM-bound Se (R = 0.51). Water-soluble Se, being the most effective component absorbed by plants, facilitates efficient uptake. Exchangeable Se, present in the outermost layer of the soil solid phase, is susceptible to plant absorption, albeit influenced by soil conditions [3; 4]. Notably, OM-bound Se primarily exists in fulvic acid and humic acid within soil humus [52]. Fulvic acid, with its relatively simple structure, can readily decompose into low-molecular-weight inorganic and organic Se compounds under alkaline conditions, offering a high potential for plant utilization. In contrast, humic acid, characterized by its high molecular  
Figure 2: Distribution of various forms of selenium (Se) in soil. weight and stable structure, poses challenges for plant absorption and utilization of Se bound to it. Conversely, no significant correlations were observed between the Se content of _G. elata_ and the sulfide-/selenide-bound Se or residual Se (R = 0.042). Selenide-/sulfide-bound Se predominantly forms in soils under strongly reducing acidic conditions, suggesting a prevailing environmental oxidation or reduction status [52]. The residual Se content is contingent upon the natural composition of minerals, often tightly bound with sulfide minerals within lattice structures. Under natural environmental conditions, these forms of Se are challenging to transform into plant-absorbable and -utilizable forms [52]. These findings suggest that an increase in water-soluble, exchangeable, and OM-bound Se in the soil correlates with an increase in Se contents in plants. Figure 3: Correlation analysis chart of _G. elata_, soil Se, and available Se. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{_G. elata_ Se} & \multicolumn{2}{c}{**Total Soil**} & \multicolumn{2}{c}{**Water-**} & \multicolumn{2}{c}{**Exchangeable**} & \multicolumn{2}{c}{**OM-Bound**} & \multirow{2}{*}{**The Rest**} & \multirow{2}{*}{**(1) + (2) + (3)**} \\  & **Se** & **Soluble (1)** & **(2)** & & & & \\ \hline _G. elata_ Se & 1 & & & & & & \\ Total soil Se & 0.11 & 1 & & & & & \\ Water-soluble (1) & 0.68 ** & 0.022 & 1 & & & & \\ Exchangeable (2) & 0.62 ** & 0.17 & 0.071 & 1 & & & \\ OM-bound Se (3) & 0.51 ** & 0.057 & 0.19 & 0.4 * & 1 & & \\ The rest & 0.042 & 0.079 ** & 0.071 & 0.091 & 0.077 & 1 & \\ (1) + (2) & 0.86 ** & 0.095 & 0.9 ** & 0.49 ** & 0.51 & 0.081 & 1 \\ (1) + (2) + (3) & 0.6 & 0.11 ** & 0.68 & 0.62 & 0.0054 & 0.095 & 0.86 ** & 1 \\ \hline \hline \end{tabular}  
* * \(p\) \(<\) 0.05; **_p_ \(<\) 0.01; “the rest” refers to the combination of selenide/sulfide combined and the residual fractions of Se; OM = organic matter.  
\end{table} 
Table 3: Correlation matrices between Se contents of _G. elata_ and cultivated soil. In this study, principal component analysis (PCA) was conducted on the pH, soil's OM content, and clay content of the soil (Table 4); from the perspective of eigenvalues, the eigenvalue of PC1 (2.4157) is significantly larger than that of PC2 (1.589), which indicates that PC1 dominates in explaining the variability in the dataset. Specifically, PC1 explained 45.434% of the variability, while PC2 explained 33.063% of the variability. The cumulative contribution shows that PC1 and PC2 together explain 78.5% of the total variability, indicating that these two principal components effectively represent most of the information in the original data.