## 2 Materials and Methods
### Experimental Design
The ferrous sulfate compensation solution contains Fe\({}^{2+}\) as reduced iron ions, which are easily oxidized to Fe\({}^{3+}\) in the soil solution, and Fe\({}^{3+}\) tends to form ferric hydroxide precipitates, limiting the availability of iron ions for plant uptake. In this experiment, the compensation solution is chelated with citric acid and the pH is adjusted to neutral with sodium carbonate before being added to the soil. The chelation of citric acid with iron forms a soluble iron complex, facilitating the mobility of iron and allowing iron ions to diffuse to the roots for plant uptake. The soil was uniformly mixed and allowed to stand until it was dry and free from muddy clumps before evenly planting _Triticum aestivum_ L. in loosened, leveled soil. The sample data collection for this experiment is primarily divided into two stages: the jointing stage and the mature stage of _Triticum aestivum_ L. growth. At the jointing stage, five _Triticum aestivum_ L. seedlings and their root soil were randomly chosen from each experimental pot and sent to the laboratory for the analyses of the total and effective iron content in the root soils and the iron content in the _Triticum aestivum_ L. roots, stems and leaves. At the mature stage, all the _Triticum aestivum_ L. seedlings were initially collected from the individual experimental pots. As the characteristics of _Triticum aestivum_ L. growth changed, the sampling parts were adjusted to include the root soil, _Triticum aestivum_ L. roots, stems, and ears (seeds with hulls). In the process of the experiment, the elevated outdoor temperatures during the grain filling stage of _Triticum aestivum_ L. partially hindered the photosynthesis of _Triticum aestivum_ L. leaves and affected the synthesis and accumulation \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Indices** & **Class A** & **Class B** & **Class C** & **Class D** & **Class E** \\  & **(Adequate)** & **(Moderately Adequate)** & **(Medium)** & **(Moderately Deficient)** & **(Deficient)** \\ \hline Available iron (mg/kg) & \textgreater{}20 & \textgreater{}10\textasci{}20 & \textgreater{}4.5\textasci{}10 & \textgreater{}2.5\textasci{}4.5 & \textasci{}2.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Grade index of available iron in soil (based on DZ/T 0295-2016 appendix D1). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Indices** & **Class A** & **Class B** & **Class C** & **Class D** & **Class E** \\  & **(Adequate)** & **(Moderately Adequate)** & **(Medium)** & **(Moderately Deficient)** & **(Deficient)** \\ \hline Available iron (mg/kg) & \textgreater{}40 & \textgreater{}15\textasci{}40 & \textgreater{}10\textasci{}15 & \textgreater{}7.2\textasci{}10 & \textasci{}4.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Grade index of available iron concentration gradient in the experimental soil. of organic matter. Meanwhile, high nighttime temperatures accelerate _Triticum aestivum_ L. respiration, resulting in increased nutrient consumption, insufficient grain filling, and reduced yield. To ensure the grain weight of the _Triticum aestivum_ L. ear sample, the test sample at the final maturity stage consists of seeds with hulls. Once the samples are collected, the plant samples are promptly separated into different parts (roots, stems, leaves, and seeds), air-dried, and then sent to the laboratory for testing.