Quantifying PSII Open Centers and Multiscale Photosynthetic Electron Transport With Solar-Induced Chlorophyll...

Area of Science:

• Plant Physiology and Photosynthesis
• Ecosystem Ecology
• Remote Sensing of Vegetation

Background:

• Accurate quantification of photosynthetic variables, such as photosystem II (PSII) open reaction centers (q_L) and electron transport rates (ETR), is vital for understanding ecosystem dynamics.
• Estimating these variables is challenging due to observational limitations and complex environmental feedbacks, especially under dynamic conditions.
• Bridging leaf-level processes to canopy-scale understanding requires robust models that can be validated across spatial scales.

Purpose of the Study:

• To develop and validate a novel SIF-qL redox model for mechanistically quantifying q_L and linear electron transport rates (J_PSII) using solar-induced chlorophyll fluorescence (SIF).
• To assess the model's accuracy and cross-scale applicability (leaf to canopy) in evergreen forest ecosystems.
• To investigate the relationship between J_PSII and q_L and identify limiting factors of electron transport.

Main Methods:

• Established the SIF-qL redox model to quantify q_L and J_PSII from SIF measurements.
• Validated the model at two evergreen forest sites (ZGT and DEJU) using continuous pulse-amplitude modulated (PAM) chlorophyll fluorescence and flux measurements.
• Evaluated model performance at both leaf and canopy scales, analyzing distinct q_L dynamics and J_PSII-q_L relationships.

Main Results:

• The SIF-qL redox model showed high accuracy in predicting leaf-level q_L at the ZGT site (R² = 0.82) but lower accuracy at DEJU (R² = 0.45).
• Leaf-level J_PSII dynamics were accurately simulated at both sites (R² = 0.92-0.97), with reliable predictive capability maintained at the canopy scale (R² = 0.62-0.71).
• Distinct q_L responses to photosynthetically active radiation (PAR) and temperature were observed, with Ribulose-1,5-bisphosphate (RUBP) generation limitations identified as dominant for J_PSII.

Conclusions:

• The SIF-qL redox model provides a mechanistic link between SIF and photosynthetic dynamics, demonstrating potential for cross-scale simulations.
• The study highlights the importance of considering species- and environment-specific factors for enhancing the model's universal applicability in ecosystem photosynthesis studies.
• Refinements are needed to improve the model's performance across diverse vegetation types and environmental conditions.