Applying Pulse Amplitude Modulation (PAM) fluorometry to microalgae suspensions: stirring potentially impacts...

Area of Science:

• * Photosynthesis research
• * Aquatic biology
• * Analytical chemistry

Background:

• * Measuring chlorophyll-a fluorescence with Pulse Amplitude Modulation (PAM) fluorometers like the Water-PAM is crucial for assessing photosynthetic efficiency.
• * Maintaining a homogeneous microalgae suspension within the emitter-detector (ED) unit is challenging due to cell settling.
• * An optional stirring accessory aims to prevent cell sedimentation during chlorophyll-a fluorescence measurements.

Purpose of the Study:

• * To investigate the impact of sample stirring on chlorophyll-a fluorescence measurements in PAM-fluorometry.
• * To understand how sample heterogeneity, induced by stirring, affects fluorescence yield during induction curve and rapid light curve analyses.
• * To identify mitigation strategies for improving the accuracy of fluorescence measurements in microalgae suspensions.

Main Methods:

• * Utilized the Water-PAM fluorometer with and without its optional stirring accessory.
• * Performed chlorophyll-a fluorescence measurements, including induction curve and rapid light curve analyses.
• * Observed the effects of cell movement and light heterogeneity within the ED unit on fluorescence yield.

Main Results:

• * The ED unit creates a vertically heterogeneous light environment, leading to varied cell quenching states within a single sample.
• * Stirring significantly influenced measured fluorescence yield by moving unquenched cells into higher light regions.
• * Cells with high sinking rates or motility exhibited similar, though reduced, issues with light heterogeneity.

Conclusions:

• * Stirring microalgae suspensions in PAM-fluorometers can introduce significant errors in chlorophyll-a fluorescence measurements due to light heterogeneity.
• * Strategies like reducing analysis time, minimizing sample volume, or controlled stirring can mitigate these errors.
• * Instrument modifications, such as a vertically oriented LED array, could provide a more homogeneous light environment and improve measurement accuracy.