Actinic light effects by ECS measurements? (Leaf Photosynthesis MultispeQ V1.0)

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Ryouichi Tanaka

Sep 2018

Hi,

If I correctly understand it, the "Leaf Photosynthesis MultispeQ V1.0" protocol starts with ECS measurements. I am afraid that it might provide actinic light effects on leaf photosynthesis and affect the subsequent measurement of Phi2, PhiNPQ and PhiNO. I am speculating this because when I compared the Phi2 measurements of "Leaf Photosynthesis MultispeQ V1.0" and those of "Chlorophyll Fluorescence (Phi2, PhiNPQ, PhiNO) v1.0- Jan" developed by Giles Johnson Lab, I found that the former protocol always gave lower Phi2 values compared with the latter. (e.g. 0.76 vs 0.57) In my understanding, the major differences of these protocols is ECS measurement.

At the same time, I guess somebody who developed the "Leaf Photosynthesis MultispeQ V1.0" protocol have already considered the actinic light effects before he/she publishes it.

Is my assumption correct? I would appreciate it if you help me clarify my concern.

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    Sep 2018

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    Nov 2023

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David M. Kramer

Sep 2018

Hi, I have not tried the Johnson protocol, but your assessment could be right if the background light is very low. The ECS measuring beam is not very bright, but that is relative to how much light you already have.

Are you using the "light_intensity" matching procedure? What ranges of light intensities are you seeing?

In any case, if you want to measure ECS, I would strongly recommend moving to the RIDES Photosynthesis protocols. They do a better job and are easier to modify for, for example, test if the ECS light pulses are affecting your Phi2.

Dave

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Ryouichi Tanaka

Sep 2018

Hi Dave, thanks a lot for your comments and suggestions. I will definitely use the RIDES Photosynthesis protocols whenever I need to measure ECS.

I am seeing at light intensities between 50-300 micromol photons m—2 s-1. So, I suppose they are not always very low. Actually, I have not noticed that I need the “light_intensity” matching procedure. Could you let me know when I need to perform it and where I can find the exact procedure?

Ryouichi

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David M. Kramer

Sep 2018

To decrease the actinic effects, you can decrease any of the following: a) the intensity; b) the duration; and/or c) the number of the measuring pulses.

Because the signals are integrated at the amplifier, the size of the signal will depend on both the duration and intensity of the LED pulses.

For the ECS measurements in the RIDES protocols, the amplitude of the measuring pulses is set using "auto_gain" which adjusts the LED brightness to match a give value. Lowering this target value will also decrease the "actinicness" of the pulses, but at a cost of decreased signal-to-noise ratio.

If you think this is a problem, why not eliminate the ECS and P700 measurements from the RIDES protocol. I think there is already a version like that, but I made a new one for you to try called

Photosynthesis RIDES no DIRKs

Dave

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Ryouichi Tanaka

Sep 2018

Thank you so much for your kind explanation and modifying the protocol for us!! I am really appriciating it!

Now that I have learned which parameters to adjust, I will try to custumize it for our own measurements.

Many thanks!

Ryouichi

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Nest Cozy

Nov 2023

Hello, I haven't experimented with the Johnson protocol, but your analysis might be accurate, especially in conditions of low background light. The brightness of the ECS measuring beam is somewhat subjective, depending on the existing light levels.

Are you employing the "light_intensity" matching procedure? What light intensity ranges are you observing?

Regardless, if your aim is to measure ECS, I highly recommend transitioning to the RIDES Photosynthesis protocols. They exhibit superior performance and are more straightforward to adapt, allowing, for instance, the assessment of whether ECS light pulses impact your Phi2. Adding the unique value, exploring RIDES Photosynthesis protocols could potentially enhance your measurement accuracy and ease of customization for specific assessments, providing a morecomprehensive solution to your needs.