Application of Simultaneous Active and Passive Fluorescence Observations: Extending a Fluorescence-Based q_L...

Area of Science:

• Plant Physiology and Photosynthesis
• Remote Sensing
• Ecology

Background:

• The fraction of open Photosystem II (PSII) reaction centers (qL) is key for linking chlorophyll fluorescence (ChlF_PSII) to electron transport rates.
• Current ChlF_PSII-qL relationships have uncertainties across plant functional types (PFTs), limiting large-scale applications.
• Accurate qL estimation is vital for mechanistic estimation of photosynthetic CO2 assimilation.

Purpose of the Study:

• To develop and validate a method for accurately estimating qL using ChlF_PSII across diverse PFTs.
• To establish quantitative ChlF_PSII-qL relationships applicable to passively induced fluorescence measurements.
• To assess the potential of remotely sensed chlorophyll fluorescence for estimating qL and improving Gross Primary Production (GPP) models.

Main Methods:

• Developed a leaf-level instrument for simultaneous active and passive chlorophyll fluorescence measurements.
• Measured light, CO2, and temperature response curves across 52 species representing seven PFTs.
• Analyzed the linear correlation between passively and actively induced ChlF_PSII and modeled the ChlF_PSII-qL relationship within PFTs.

Main Results:

• A strong linear correlation (R2 = 0.85) was found between passively and actively induced ChlF_PSII.
• The ChlF_PSII-qL relationship parameters varied among PFTs, but ChlF_PSII reliably modeled qL within each PFT (R2 = 0.85–0.96).
• Quantitative ChlF_PSII-qL relationships were established for various PFTs using passively induced fluorescence.

Conclusions:

• Passively induced fluorescence can be reliably used to calculate ChlF_PSII for estimating qL.
• This study provides PFT-specific ChlF_PSII-qL models, improving the accuracy of qL estimation.
• Remotely sensed chlorophyll fluorescence shows significant potential for mechanistic GPP estimation at large spatial scales.