## 3 Results and Discussion
### Influence of Soil Properties on Zn Absorption by Rice Grains  
The Zn content in rice grains is influenced by various factors. As shown in Figure 3, there is no significant correlation between the Zn content in the rice grains and the Zn \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \begin{tabular}{c} **Sample** \\ **Distribution** \\ **Area** \\ \end{tabular} & \begin{tabular}{c} **Sample** \\ **Size** \\ \end{tabular} & \begin{tabular}{c} **Type** \\ **Type** \\ \end{tabular} & \begin{tabular}{c} **Min Value** \\ **(mg/kg)** \\ \end{tabular} & \begin{tabular}{c} **Max Value** \\ **(mg/kg)** \\ \end{tabular} & \begin{tabular}{c} **Mean Value** \\ **(mg/kg)** \\ \end{tabular} & \begin{tabular}{c} **Median Value** \\ **(mg/kg)** \\ \end{tabular} & \begin{tabular}{c} **Coefficient** \\ **of Variation** \\ \end{tabular} \\ \hline \multirow{3}{*}{\
\begin{tabular}{c} Heyuan Region \\ \end{tabular} } & \multirow{3}{*}{65} & Root Soil & 32.00 & 156.70 & 72.30 & 68.40 & 0.32 \\ \cline{2-6}  & & Rice Grains & 13.60 & 25.40 & 18.47 & 18.40 & 0.15 \\ \cline{2-6}  & & \(\text{BAF}_{\text{Zn}}\) & 0.10 & 0.67 & 0.28 & 0.25 & 0.35 \\ \hline \multirow{3}{*}{
\begin{tabular}{c} Pearl River Delta \\ \end{tabular} } & \multirow{3}{*}{306} & Root Soil & 16.90 & 253.30 & 79.78 & 71.32 & 0.49 \\ \cline{2-6}  & & Rice Grains & 11.33 & 30.37 & 18.10 & 17.73 & 0.16 \\ \cline{1-1} \cline{2-6}  & & \(\text{BAF}_{\text{Zn}}\) & 0.06 & 1.19 & 0.31 & 0.26 & 0.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Zn content and \(\text{BAF}_{\text{Zn}}\) of rice grains and root soil in study area. Figure 3: The relationship between soil Zn and rice Zn in different regions. content in the root soil, indicating that the Zn content in the rice grains is not simply determined by the Zn content in the soil. Instead, it is closely related to the bioavailable form of Zn in the soil [43] and other physicochemical properties of the soil. The relationship between the soil properties and the bioaccumulation factor of Zn (BAF\({}_{\text{Zn}}\)) in the rice was evaluated using [PERSON]'s correlation coefficient (Figure 4). The data were log-transformed to approximate a normal distribution. The results show that the BAF\({}_{\text{Zn}}\) is negatively correlated with sulfur (S) (\(r=-0.45\)), phosphorus (P) (\(r=-0.53\)), calcium oxide (CaO) (\(r=-0.75\)), manganese (Mn) (\(r=-0.72\)), total iron (TFe\({}_{2}\)O\({}_{3}\)) (\(r=-0.78\)), and total organic carbon (TOC) (\(r=-0.65\)) and positively correlated with SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) (\(r=0.69\)). BAF\({}_{\text{Zn}}\) has a strong correlation with CaO, Mn, and TFe\({}_{2}\)O\({}_{3}\) and a moderate correlation with P, TOC, and SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\). Sulfur (S) can form insoluble zinc sulfide (ZnS), reducing the bioavailability of Zn in the soil [44; 45]. In flooded paddy soils, the redox potential is low, and sulfur is often reduced to S\({}^{2-}\), which reacts with Zn\({}^{2+}\) to form ZnS precipitates, reducing the mobility of Zn in the soil [46; 47]. In addition to the above redox reactions, sulfur-containing organic compounds in the soil can form covalent bonds with heavy metals, playing a significant role in the activation and fixation of heavy metals. The TOC content is used as an indicator of the soil organic matter content [48]. In general, the mobility and bioavailability of heavy metals increase as the organic matter content decreases [49]. Organic matter in the soil contains a variety of components, including abundant ligands or functional groups such as carboxyl (-COOH), hydroxyl (-OH), and phenolic hydroxyl groups (aromatic ring-OH), which can form complexes with metal ions and affect the migration and transformation of heavy metals [50]. Calcium oxide (CaO) is an effective buffering agent in soil. Increasing soil CaO raises soil pH [51], promoting the formation of the carbonate and hydroxide precipitates of heavy  
Figure 4: Correlation heatmap between soil properties and BAF\({}_{\text{Zn}}\).