1：Experimental Design and Method Selection:

The study modified the PROSPECT-5 model by incorporating copper content and estimating the specific absorption coefficient (Kcu) for copper. The methodology involved estimating leaf structure parameters (N) using reflectance in 400-510 nm to avoid copper absorption influence, and fitting Kcu using a merit function minimization approach.

2：Sample Selection and Data Sources:

Used 33 groups of datasets from copper-stressed wheat and pak choi leaves grown in controlled experiments with varying copper levels (25 to 4800 mg/kg in soil). Samples were divided into 22 for calibration and 11 for validation. A public dataset LOPEX93 was also used for comparison.

3：List of Experimental Equipment and Materials:

ASD FieldSpec FR spectroradiometer with Li-1800 integrating sphere, halogen lamp, spectrophotometer for pigment measurement, atomic absorption spectrophotometer for copper content, scanning electron microscope (KYKY-EM 3200), plastic pots, copper sulfate solutions, and various chemicals for biochemical analysis.

4：Experimental Procedures and Operational Workflow:

Plants were grown in copper-treated soil, spectral reflectance was measured using the spectroradiometer and integrating sphere, biochemical contents were measured post-reflectance using chemical methods, and SEM images were acquired for structural analysis. Data processing involved estimating N and Kcu, and validating the model with RMSE calculations.

5：Data Analysis Methods:

Statistical analysis including mean, standard deviation, coefficient of variation, and root mean square error (RMSE) for comparing simulated and measured spectra. Specific absorption coefficients were estimated using minimization of merit functions.