Briefly, these 3 parameters describe the destination of captured light, and the sum of all 3 parameters should equal 1.0:

Phi2: Quantum yield of Photosystem II. This measurement is essentially the percentage of incoming light (excited electrons) that go into Photosystem II (photosynthetic processes). Photosystem II is where most light energy is converted into food.

PhiNPQ: Ratio of incoming light (excited electrons) that goes towards non-photochemical quenching. The plant regulating excess energy in such a way as too reduce damage to the plant.

PhiNO: Ratio of incoming light that is lost via non-regulated processes. PhiNO is the combination of a number of unregulated processes whose by products can inhibit photosynthesis or be harmful to the plant.

Also, the paper which best describes many of these parameters is here:

http://www.ncbi.nlm.nih.gov/pubmed/16228395

Thanks everyone -- this was very helpful!

Dynamics of "PhiNPQ" "NPQt" is similar, a positive correlation. "PhiNO" and "NPQt" - a negative correlation. "PhiNO" and "Phi2" - a positive correlation. Is it true?

The dynamics of PhiNPQ and NPQt will always be similar. However, the relationship between PhiNPQ (and NPQt) and Phi2 and PhiNO is not always similar.

If PhiNPQ increases, then there must be a corresponding decrease in either Phi2 or PhiNO, because the sum of PhiNPQ + Phi2 + PhiNO =1. However, it could be that only Phi2 goes down to compensate for increased PhiNPQ and PhiNO doesn't change, or vice versa. So we cannot assume a positive or negative correlation.

Put another way, while we've seen some general trends so far for Phi2 PhiNPQ and PhiNO, exploring these relationships remains an open and very compelling path - there is science to be done here!!!

:)

Greg

I know this was written six years ago--hopefully someone can respond! What is the exact difference between PhiNPQ and NPQt? I have these two measurements and they both have a positive correlation. I am trying to explain each parameter in my thesis. Thank you!!

You may refer to Tietz et al., 2017 doi:10.1111/pce.12924

Hi Gabriella,

for the PhiNPQ parameter (and for the PhiNO for that matter), please have a look at Kramer et. al 2004. PhiNPQ describes the yield of downregulatory processes, like Phi2 for photosystem II. NPQt, like NPQ is the extent of non-photochemical quenching. As Tewodros already mentioned you can find that derivation of that parameter in Tietz et al 2017.

Kramer, D. M., Johnson, G., Kiirats, O. and Edwards, G. E. (2004) New Fluorescence Parameters for the Determination of QA Redox State and Excitation Energy Fluxes. Photosynth Res 79, 209.

I hope this helps ~Sebastian