Lin et al. (2025) Linking the diurnal and seasonal dynamic of photochemical reflectance index and photosynthesis in a paddy rice field

Identification

• Journal: Smart Agricultural Technology
• Year: 2025
• Date: 2025-12-31
• Authors: S. Lin, Jingwen Lai, Gaofei YIN, Junyong Fang, Xue Liu, X. H. Zhang, Hao Yang, Peiqi Yang, Qing Xiao
• DOI: 10.1016/j.atech.2025.101775

Research Groups

• Guangdong Province Data Center of Terrestrial and Marine Ecosystems Carbon Cycle, School of Geography and Planning, Sun Yat-Sen University, Guangzhou, China
• Faculty of Geosciences and Engineering, Southwest Jiaotong University, Chengdu, China
• National Engineering Laboratory for Satellite Remote Sensing Applications, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
• Key Laboratory of Quantitative Remote Sensing in Agriculture of Ministry of Agriculture and Rural Affairs, Information Technology Research Center, Beijing Academy of Agriculture and Forestry Sciences, Beijing, China
• Key Laboratory of Virtual Geographic Environment, Ministry of Education, Nanjing Normal University, Nanjing, China
• Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing, China

Short Summary

This study developed a low-cost, ultra-spatial resolution multispectral camera to obtain high-frequency photochemical reflectance index (PRI) observations in a paddy rice field. It demonstrated that separating PRI into seasonal (PRI0) and diurnal (PRId) components effectively links PRId to light use efficiency (LUE) and captures atmospheric dryness stress on plant photosynthesis, with a significantly improved correlation compared to PRI alone.

Objective

• To develop an economical, ultra-spatial resolution multispectral camera for high-frequency Photochemical Reflectance Index (PRI) observations in a paddy rice field.
• To explore the diurnal relationship between Light Use Efficiency (LUE) and the diurnal change of PRI (PRId) in a paddy rice field.
• To investigate whether PRId can accurately reproduce physiological stress on photosynthesis in a paddy rice field with sufficient soil water supply.

Study Configuration

• Spatial Scale: Leaf-scale to canopy-scale observations (ultra-high spatial resolution, less than 10 cm spatial resolution, 2048 × 3072 pixels). Camera mounted on a 2-meter height tower, oriented southeast with a 60° viewing zenith angle. Study site: Honghe farm (133.51°E, 47.59°N), Jiamusi, Heilongjiang province, China.
• Temporal Scale: Diurnal (30-minute intervals from 5:00 to 17:00 local time) and seasonal (April 23rd to October 30th, 2023).

Methodology and Data

• Models used:
  • SMARTS (Atmospheric Radiative Transfer of Sunshine) model for 1-nanometer solar energy incident spectra.
  • Daytime partitioning method for separating net ecosystem exchange (NEE) into gross primary production (GPP).
  • Empirical GPP model: GPP = a × VI × PAR + b.
• Data sources:
  • Custom-developed multispectral rotating camera (WMS6, China) for reflectances at 531, 570, 660, 705, 750, and 860 nanometers.
  • Integrating sphere (Labsphere XTH-2000C) for camera radiometric calibration.
  • LI190r Quantum Sensor (LI-COR CO., LTD., USA) for downwelling photosynthetic active radiation (PAR).
  • In situ eddy covariance measurements (Li-7500, LI-COR CO., LTD., USA) for 30-minute net ecosystem exchange (NEE) of CO₂ fluxes.
  • Meteorological data: air temperature (Ta, in °C), vapor pressure deficit (VPD, in hPa), soil water content (SWC, in m³ m⁻³), and shortwave downwelling radiation (SW, in MJ).
  • MODIS leaf area index (LAI) product (MCD15 LAI).

Main Results

• The developed low-cost (~12,000 USD) multispectral rotating camera system successfully acquired high-frequency, ultra-high spatial resolution PRI observations.
• The diurnal change of PRI (PRId), derived by separating PRI into early morning PRI (PRI0) and diurnal variation, effectively tracked the diurnal cycle of LUE.
• The coefficient of determination (R²) between PRId and LUE was 0.65 during the greening-up period, significantly higher than that between PRI and LUE (0.46).
• PRId successfully captured the physiological stress induced by atmospheric dryness (VPD) on plant photosynthesis, showing an increase as VPD increased (R² = 0.25).
• LUE decreased as VPD increased, exhibiting a significant negative correlation (R² = 0.33).
• Soil water content (SWC) had only a marginal influence on both LUE and PRId, indicating that photosynthesis was not soil water-limited under the flooded conditions of the paddy rice field.
• Chlorophyll-related vegetation indices (CIr and NDVI) showed strong relationships with seasonal GPP (e.g., CIr × PAR R² > 0.5), but CIr and its diurnal change (CIrd) did not effectively track diurnal LUE or VPD changes. PRI0 was not suitable for estimating GPP during planting and maturity periods.

Contributions

• Development of a low-cost (~12,000 USD) ultra-spatial resolution (< 10 cm) multispectral rotating camera system for continuous, high-frequency (30-minute) PRI observations, addressing limitations of existing proximal remote sensing methods.
• Successful application of the PRI separation method (PRI0 for seasonal, PRId for diurnal) to a cropland (paddy rice field), demonstrating its effectiveness in linking PRI to LUE and physiological stress, an area previously underexplored in cropping systems.
• Demonstrated that PRId effectively tracks diurnal LUE and atmospheric dryness-induced physiological stress in paddy rice, even under conditions of sufficient soil water supply.
• Proposed and implemented a robust data quality control approach to mitigate the effects of atmospheric noise, data volume, and radiometric calibration on high-frequency PRI measurements.

Funding

• National Natural Science Foundation of China (Grant number No 42371373, 42101319)
• National Key Research and Development Program of China (Grant No 2023YFF1303602)
• Science and Technology Program of Guangdong (No. 2024B1212070012)

Citation

@article{Lin2025Linking,
  author = {Lin, S. and Lai, Jingwen and YIN, Gaofei and Fang, Junyong and Liu, Xue and Zhang, X. H. and Yang, Hao and Yang, Peiqi and Xiao, Qing},
  title = {Linking the diurnal and seasonal dynamic of photochemical reflectance index and photosynthesis in a paddy rice field},
  journal = {Smart Agricultural Technology},
  year = {2025},
  doi = {10.1016/j.atech.2025.101775},
  url = {https://doi.org/10.1016/j.atech.2025.101775}
}