Curious as to your definition of "burst of high intensity".
How much more light than normal would the constitute a burst?
Well, the sun's PPFD can go up to 1700umol (even more), yet the question is, which wavebands have all been included? Such a burst of PAR 400-700nm would most likely do some damage to leaves (without CO2 supp) - esp. when wavelengths are used, which are swiftly - or efficiently - absorbed by the pigments or proteins (UV, blue, red).
At higher ppfd green & FR would make more sense, better yet: be less destructive.
Both these colors add very much to the ambient light, they hold a good penetration power, are either deflected or transmitted occasionally, and green can cause fluorescence.
Another mechanism which happens at high ppfd levels - and which further adds to the penetration - is chloroplast movement inside the cells of a leaf - and also leaf rearrangement. Both of which can be regarded as plant training - and which may also increase the strength/numbers of sub-canopy shoots - and their strength - as they temporarily get more light - in a fluctuative high-ppfd/ low-ppfd environment - compared to a average-ppfd env.
There is research that shows pulsed UV to be more effective than continuous UV.
Spot on!
Establishing methods to circumvent the "getting used to" the UV.
Am I reading this wrong?
The paper says they used UVA lamps
"Supplemental UV radiation treatments began 8 weeks after sowing seed and was provided by Q-Panel UVA-340 bulbs "
Well, the 340 lamp does put out some UVB.
This one, and their "brothers and sisters" have specific spectra designed to mimick the sun's natural output:
In the .pdf it's stated they did also use some foliage/mylar to block unwanted wavebands - but this lamp is good to further stimulate the 310nm & 365nm response.
But they also give scientists the ability to raise the level (and, at that, naturally...)
You can read more about this here:
LINK
"Our results show that neither supplemental UV-A nor supplemental UV-A+B strongly affected the biosynthesis of potentially beneficial phytochemicals including carotenoids and phenolic compounds "
Well, there are a lot of carotenoids, but the study mentiones ß-carotene - which is actually build up in response to
blue-light:
In leaves, ß-carotene acts as a molecule to dissipate excess heat
away from the light-harvesting-complexes - thus, it sits very much at the outside of the chlorophyl-complexes. Actually, it does also capture light, but not submit this energy into the photosynthetic process - just turn it to heat (which may be bad under a lot of circumstances...)
In this diagram you can see the drop of the photosynthetic work due to the absorption band of the carotenes: (between 450-500 in PSI)
^^ this is actually the reason why modern LED tech willfully creates this "
cyan-gap" - to make it easier for the chloroplasts to dissipate excess heat - esp. from wavelengths 380-450nm.
The study you uploaded however was still very interesting - and not inconclusive - as
Rutin (Quercetin) is a compound that holds alot of beneficial qualities for humans. A lot of superfoods contain it, and it works quite well as an immun-booster against certain diseases.
I guess one of the reasons why some results couldn't be brought in by the study was the supplement by HPS lamps which greatly lack the blue light.