Analysis of Cadmium Contamination in Lettuce (Lactuca sativa L.) Using Visible-Near Infrared Reflectance Spectroscopy
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials and Experimental Design
2.2. Spectral Data Acquisition
2.3. SPAD Value Determination
2.4. Leaf Cadmium Content Determination
2.5. Data Processing and Analysis
2.5.1. Data Processing Methods
2.5.2. Calculation Method for Spectral Characteristic Parameters
3. Results and Discussion
3.1. Effects of Cadmium Stress on the Biochemical Parameters of Lettuce
3.1.1. Effects of Cadmium Stress on the SPAD Value of Lettuce
3.1.2. Effects of Cadmium Stress on Cadmium Content in Lettuce Leaves
3.2. Analysis of Spectral Response Characteristics of Lettuce Leaves under Cadmium Stress
3.2.1. Differential Analysis of Visible-Near Infrared Spectra
3.2.2. Analysis of Spectral Characteristic Parameters in Lettuce Leaves
3.2.3. Analysis of Normalized Difference Vegetation Index (NDVI705) at the Red Edge
3.3. Correlation Analysis between Spectral Characteristic Parameters, Leaf Cadmium Content, and SPAD Value
3.4. Establishment of a Leaf Cadmium Content Inversion Model for Lettuce under Cadmium Stress
3.5. Model for SPAD Value Inversion in Lettuce Leaves under Cadmium Stress
3.6. Model Validation
4. Conclusions
- (1)
- Under cadmium stress, the SPAD values of the lettuce leaves exhibited inhibition at high concentrations and promotion at low concentrations. Moreover, the cadmium concentration in the lettuce leaves increased with increasing soil cadmium concentrations.
- (2)
- The red edge, red valley, and green peak positions in the reflectance spectra of the lettuce leaves were sensitive to cadmium stress. Under cadmium stress, these positions shifted, and they could be used for preliminary diagnosis of cadmium pollution in lettuce. The normalized difference vegetation index of the red edge (NDVI705) was lower than the CK group under 10 mg/kg and 20 mg/kg cadmium stress, indicating that lettuce growth was affected by the cadmium stress.
- (3)
- The models corresponding to SDr/SDy and (SDr − SDy)/(SDr + SDy) can effectively estimate the cadmium content in lettuce leaves. The models corresponding to NDVI705 and Pg/Pr can accurately estimate the SPAD values of lettuce leaves.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
Correction Statement
References
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Feature Parameter | Parameter Description | Wavelength/nm |
---|---|---|
Pg (Peak green value) | Maximum value of leaf reflectance spectrum | 500~600 |
Vr (Depth of red valley) | Minimum value of leaf reflectance spectrum | 600~720 |
Pr (Red shoulder amplitude) | Maximum value of leaf reflectance spectrum | 750~950 |
Λr (Red edge position) | Wavelength corresponding to the maximum value of the first-order derivative of the leaf reflectance spectrum | 670~780 |
Dr (Amplitude of red edge) | Maximum value of the first-order derivative of the leaf reflectance spectrum | 670~780 |
Drmin (Minimum amplitude of red edge) | Minimum value of the first-order derivative of the leaf reflectance spectrum | 670~780 |
Dy (Amplitude of yellow edge) | Maximum value of the first-order derivative of the leaf reflectance spectrum | 560~640 |
Db (Amplitude of blue edge) | Maximum value of the first-order derivative of the leaf reflectance spectrum | 490~530 |
SDr (Red edge area) | Sum of the first-order derivative of the leaf reflectance spectrum | 670~780 |
SDy (Yellow edge area) | Sum of the first-order derivative of the leaf reflectance spectrum | 560~640 |
SDb (Blue edge area) | Sum of the first-order derivative of the leaf reflectance spectrum | 490~530 |
SDr/SDy | Red edge area/yellow edge area | / |
SDr/SDb | Red edge area/blue edge area | / |
SDb/SDy | Blue edge area/yellow edge area | / |
(SDr − SDy)/(SDr + SDy) | Normalized value of red edge area and yellow edge area | / |
(SDr − SDb)/(SDr + SDb) | Normalized value of red edge area and blue edge area | / |
(SDb − SDy)/(SDb + SDy) | Normalized value of blue edge area and yellow edge area | / |
NDVI705 (Normalized vegetation index of the red edge) | R750 and R705 represent the spectral reflectance values at 750 nm and 705 nm, respectively | |
Dr/Drmin | Amplitude of red edge/minimum amplitude of red edge | / |
Pg/Pr | Peak green value/red shoulder amplitude | / |
Dr/Dy | Amplitude of red edge/amplitude of yellow edge | / |
Dr/Db | Amplitude of red edge/amplitude of blue edge | / |
Dy/Db | Amplitude of yellow edge/amplitude of blue edge | / |
Cadmium Treatment | Seedling Stage | Growth Stage | Mature Stage | ||||||
---|---|---|---|---|---|---|---|---|---|
Red Edge Position/nm | Green Peak Position/nm | Red Valley Position/nm | Red Edge Position/nm | Green Peak Position/nm | Red Valley Position/nm | Red Edge Position/nm | Green Peak Position/nm | Red Valley Position/nm | |
CK | 702 | 551 | 676 | 693 | 548 | 677 | 702 | 550 | 671 |
Cd1 | 702 | 551 | 676 | 693 | 548 | 678 | 702 | 550 | 671 |
Cd5 | 702 | 548 | 673 | 693 | 548 | 676 | 702 | 551 | 671 |
Cd10 | 702 | 551 | 670 | 693 | 548 | 670 | 693 | 551 | 676 |
Cd20 | 702 | 551 | 670 | 693 | 547 | 676 | 702 | 547 | 676 |
Spectral Characteristic Parameters | Fitting Model | R2 | Significance | F |
---|---|---|---|---|
SDy | 0.535 | * | 4.223 | |
SDb | 0.431 | * | 4.545 | |
SDr/SDy | 0.872 | ** | 24.959 | |
SDb/SDy | 0.781 | ** | 13.041 | |
(SDr − SDy)/(SDr + SDy) | 0.792 | ** | 13.996 | |
(SDb − SDy)/(SDb + SDy) | 0.65 | ** | 6.800 | |
Dr/Dy | 0.463 | * | 5.178 |
Spectral Characteristic Parameters | Fitting Model | R2 | Significance | F |
---|---|---|---|---|
Pg | 0.677 | ** | 12.569 | |
NDVI705 | 0.789 | ** | 22.407 | |
Pg/Pr | 0.755 | ** | 40.009 |
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Zhou, L.; Zhou, L.; Wu, H.; Kong, L.; Li, J.; Qiao, J.; Chen, L. Analysis of Cadmium Contamination in Lettuce (Lactuca sativa L.) Using Visible-Near Infrared Reflectance Spectroscopy. Sensors 2023, 23, 9562. https://doi.org/10.3390/s23239562
Zhou L, Zhou L, Wu H, Kong L, Li J, Qiao J, Chen L. Analysis of Cadmium Contamination in Lettuce (Lactuca sativa L.) Using Visible-Near Infrared Reflectance Spectroscopy. Sensors. 2023; 23(23):9562. https://doi.org/10.3390/s23239562
Chicago/Turabian StyleZhou, Lina, Leijinyu Zhou, Hongbo Wu, Lijuan Kong, Jinsheng Li, Jianlei Qiao, and Limei Chen. 2023. "Analysis of Cadmium Contamination in Lettuce (Lactuca sativa L.) Using Visible-Near Infrared Reflectance Spectroscopy" Sensors 23, no. 23: 9562. https://doi.org/10.3390/s23239562