Visible light is that part of the electromagnetic (EM) spectrum which humans can see with the naked eye. However, the EM spectrum extends far to the left and right of the visible light spectrum, for example, moving to the right of violet we encounter ultraviolet radiation, then X-rays and then gamma-rays. Moving to the left we encounter infrared radiation, then radio waves and then microwaves. All these forms of electromagnetic radiation, from microwaves to visible light to gamma-rays are waves of electrical and magnetic energy. Plant pigment molecules absorb only light in the wavelength range of 700 nm to 400 nm; this range is referred to as photosynthetically-active radiation.Wavelengths above 750 nm correspond to infrared light and beyond. Green plants do not utilise this infrared light directly for photosynthesis, but purple bacteria do. The two peak colours absorbed by plants for photosynthesis, are around 450 nm or blue light and 670 nm or red light.

Far red light influences phytochrome, which has many functions such as germination, flowering, shade avoidance, chlorophyll synthesis, etc. See: http://www.canna-uk.com/effect-of-red-and-far-red-light-on-flowering for a description of how red and far red light influence phytochrome ratios and how these affect physiological functions :)

One should refer to action spectrum and as far i know above 700nm the yield is marginal. Inside antennas there would be some transfer uphill to PS2 but it would depend on some residual pigment form in PS1. Action spectrum in McCree Ag Met 1972 and BBA 2005 by Pettai et al. for Fred effects are available on network.

Dear Alexei,

as shown for Arabidopsis, the PSI antenna binds the so-called red chlorophylls (chlorophylls that have their absorption maxima at longer wavelengths than the primary electron donor P700). You may find some details in:

Jensen PE, Bassi R, Boekema EJ, Dekker JP, Jansson S, Leister D, Robinson C, Scheller HV (2007) Structure, function and regulation of plant photosystem I. Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1767 (5): 335-352

Best Regards,

Carlo.

Solar radiation is absorbed by leaves beyond the PAR but that doesn't mean this energy is used for photosynthesis. Leaves contain water and the absorption spectrum of water is very high in this waveband.

Absorption at the far end of the EM spectrum does not translate to photosynthetic activity. The ability to absorb such wavelengths that are not photosynthetically active may be an adaptive mechanism. The energy will be dissipated if not utilised. However, the absorbed energy has other activities within the system beyond strict Photosynthetic productivity. The influence on plant growth and development however can not therefore be discountenanced as separate systems such as phytochrome induction and action which are crucial are wholly dependent on longer wavelength radiation

Dear All: thank you so much for you insights! Indeed, the coommon belief is that the radiation absorbed outside the PAR region does not contribute much to actual photosynthesis. However AFAIK this conclusion is deduced from the action spectra recorded with a single monochromatic excitation. But in real life this is not the case (we have PAR absorbed + addendum in the NIR). Any idea on this?

Concerning the question: Why do plants absorb..........:

Because they are plants and in terms of evolution they are much older than mankind.

Evolution means: increasing survival chance in the given environment with the given resources (biochemically and energetically).

What means: well beyond the end of the "visible" range (>700nm)? The visible spectrum for who: The plant or the Homo Sapiens?

As Humanity is much younger than the plants we could well mutate, after a long while, to green looking beings. Two families of "Greenhorns" with a different evolution.

What has to become changed: The visible spectrum of the eye or the pigments of the plants?

Let's see and see you then, but not in a - green and red- flowering

poppy-field, as we know it "today" from the famous painting.

Regards,

Reto

[email protected]

Alexei,

You make a very valid point: the common action spectrum of photosynthesis as reported by McCree and others looked at the action of individual wavelengths. We published a paper last year (see Article Far-red light is needed for efficient photochemistry and pho...

Check this

https://www.sciencedirect.com/science/article/pii/S0005272805001192

Which concludes there maybe a small amount of far-red pigment. Also it suggests uphill energy transfer is possible in PSII through vibronic energy states. It should be remembered that photosynthetic organism have many ways of adapting to environmental condition so it wouid not be a surprise if under certain conditions it attempts to utilize far-red light.

..,.......This is true, dear colleague. As long as the plants can use far-red light it's better that they do not ask us first for a permission to do so.....

Human are not photosynthetic organisms, but like to be close to a stove:

"......et habeat bonam pacem, qui sedet post fornacem." Try it. Best regards.

Reto J. Strasser

I don’t understand this long discussion, as some developments obviously neglect basic physics and already well established experimental data. The molecular mechanism of photosynthesis can operate only with light absorbed by chlorophyll (cf. Einstein law), directly or through energy transfer from accessory pigments, when they exist. Chlorophyll a does not absorb above 700-740 nm (PS1), so any biological effect operating beyond this value is due to other mechanisms. For example, it may be plant growth and development controlled by phytochrome, as mentioned by others, or leaf heating through infra-red absorption, mainly by water: this is an important parameter in near —and a fortiori above— light-saturated photosynthesis. Also, one should remember that what is called light (gross) “absorption” is the difference between incoming light on one side and outcoming light on the other, that actually results from true absorption but also from light scattering.

My deep thanks to those who joined the discussion! Just few notes. It is true that chlorophyll dissolved e.g. in acetone has only a little, if any at all, measurable absorption beyond 700 nm. But absorption of Chl (and other pigments) in situ is a different story. Essentially, the question is, what is the contribution of the energy captured (?) outside the visible range to the energy budget of the plant. Sure one needs to distiguish true (chromophore) absorption from escape of light from detection due to scattering by a leaf (see e.g. Article Does a leaf absorb radiation in the near infrared (780-900 n...

Does the ability to capture light & drive photosyntheis by "conventional" Chl (not the bateriochlorophyll) give the plants any competitve advantage or it is just a "side effect" of the "mainstream" evolution of the photosynthetic apparatus?..

An interesting read in cyanobacteria: https://www.sciencealert.com/new-chlorophyll-role-photosynthesis-converts-near-infrared-cyanobacteria

Good question: If you bake a birthday cake, and if it is not black....then it is yellow. Why, because I see it as yellow. The cat may see it differently with her night sensitive vision. We call it yellow because already other objects are reflecting these wavelengths to our eyes and we learnt from the parents that this is yellow, a very subjective sensation. That's the reason that objective spectra became measurable with "non thinking and non feeling machines" which however supply reproducible spectra. Mixtures of clean colored solutions (e.g. blue and yellow) may give us a sensation of GREEN, without any green molecule (spectroscopically) in the solution. Colours can be seen like MIRAGES in the desert, not by mirror effects, but by light mixing effects in our brains. This way a Zebra with blue and yellow stripes will remain for us a stripped Zebra and not a green animal...…..The Italian proverb says: Se non è vero, è ben trovato (If it isn't true, it's well invented...).

Best regards, Reto

If our eyes do not see a color, it does not mean that there is any color, we just do not see it due to our vision system based on Rhodopsine which is "blind" in the far red, even so far red light is warming up nearly every thing....

Regards,

Reto

Every thing which gets warm in a warm night is absorbing in the near far red etc, we just do not see it with our eyes.

Reto

Absorption of light by plants between the wavelength 750 - 850 nm is important. This is where plant phytochromes absorb to sense red:farred intensity ratios and the presence of a shaded environment. In so doing they can switch on or off the expression of genes for flowering, seeding and stem elongation among many other things.

In addition to my previous comment, you may perhaps pay an attention to the following point. You are talking of higher plant leaves and IR absorption. I do not know how the latter is measured but, some outcoming light in line with the incident beam escapes direct detection due to significant light scattering (this may be overcome using a so-called intergrating sphere). Besides, there are other substances than chlorophyll(s) in a plant leaf that absorb light, including water itself in the near IR range (at 760 and 970 nm) and above (1.19, 1.45, and 1.94 µm).

Yes, we did consider this:

https://link.springer.com/content/pdf/10.1023/A:1019823303951.pdf

Still there is a significant retention of energy in the NIR by leaves. We doing some experiments now to clarify this. Thank you!

Evolution does not function to approach the maximal possible absorption of light, then every thing would be BLACK for our eyes and even more, every thing would absorb anywhere from UV to FAR RED. The vegetables would "grow" this way in an already boiled form.....The trick in evolution is to find an OBTIMAL behaviour to survive first and secondly to survive in an optimal way. That's why most ORCHIS do not grow in your garden spontaneously, if you are not living in a tropical forest. So how to survive? just by trying different life styles in your given environment. The one who survives and adapts has an advantage towards non adapted "IMIGRANTS". If these "visitors" get not adapted to the new situation they have to cope with. If there is no looser and no winner, the population DIVERSITY will increase, which gives the best chance to adapt und survive unexpected situations. Physical FORCE is an advantage, but not a guarantee to be the winner in the next SELECTION, where the contrahend is not stronger by FORCE but smarter by BRAIN, which leads to SUSTAINABILITY, based on an adaptable HETEROGENEITY within a population. Behaving SMART and STRONG increase the surviving chance for an individuum within a changing environnement…However, all that needs time, a lot of time. That's why: CARPE DIEM for the time which will be given to you. Good luck.

[email protected]

Is it possible that as living organisms probably first evolved in water, they adjusted to the spectrum they get in water, which loses quite a bit of the shorter wave lengths?

I would question the idea that plants absorb light in the NIR as most of it is either reflected or transmitted by the leaf. Only a small amount need be absorbed here by phytochromes to control gene expression. The IR part is absorbed strongly by water and has nothing to do with photosynthesis apart from perhaps heating up the plant so that some biochemical reactions may become more efficient.

Thanks to the colleagues who gave excellent statements to quite difficult questions. Hopefully many students will read the lines which do not appear in text books. In terms of light we always have to do with photons and single photon absorption events by absorbing pigments. Overheating is often a problem in summer and in the deserts with lack of water. However you seldom see an overheated Cactus. As you see seldom a 4 leg Camel in the swiss mountains. Apparently they "learnt" how to behave and exploit harmonically the resources and where to go on our planet EARTH. Did the homo sapiens, with his huge brain, demonstrate a similar intelligence? Let's see who survives in the long run. New York or the termites and ants in their "apartment buildings?"

Best regards; Reto J. Strasser "[email protected]"

Yair, interestingly Acaryochloris marina Cyanobacteria uses far red region of the spectrum due to unique chlorophyll d molecule and few more organisms due to the presence of chlorophyll f. Article Photosynthesis at the far-red region of the spectrum in Acar...

However, plant mostly uses Far red for phytochrome based signaling for photo-morphogenesis using Pfr and Pr molecular forms.

In the lab literature, chl a and b absorption is reported to act up to 700 nm. In field observations chl absorption is happening well beyond 700 nm, and as shown by Gitelson in several papers, and very effective vegetation indices are using NIR and far-red bands around 740 nm to monitor canopy chlorophyll. Also in Radiative Transfer Models such as Prosail, chlorophyll is driving absorbance up to 760 nm. The interesting question is how come very different results can be obtained in the lab and in vivo? What is the physical basis for this?

Far-red and red-light absorption oscillations contribute to plant photoperiodic responses, photomorphogenesis, bolting and circadian rhythms.

https://www.khanacademy.org/science/biology/photosynthesis-in-plants/the-light-dependent-reactions-of-photosynthesis/a/light-and-photosynthetic-pigments

Alexei Solovchenko

Plant leaves and human cells are biological quantum materials.

The term quantum materials refers to materials whose properties are principally defined by quantum mechanical effects at macroscopic length scales (emergent property) and that exhibit phenomena and functionalities not expected from classical physics.

Photosynthesis is an emergent property of a leaf. The transmission of information from the virus to the cell is an emergent property of the cell. They were created through a long evolution, starting from the simpler water quantum materials that we study. These are micellar solutions of ionic surfactants in the region of the phase transition of the formation of spherical micelles or the liquid/liquid water transition. Such studies lead to knowledge of the quantum behavior of systems "from below" and give a clearer understanding of such concepts as quantum fluctuations, zero point of water, О-Н, С-Н bonds, thermal fluctuations, tunneling, coherence, entanglement.

Thesis Mirgorod Yuri. QUANTUM NUCLEAR EFFECT IN AQUEOUS IONIC SURFA...

Preprint Nuclear quantum effect in aqueous micellar surfactant solutions

Preprint Supplementary information for Nuclear quantum effect in aque...

The experts of this post have a closer approach to the problem "from above".

https://www.esalq.usp.br/lepse/imgs/conteudo_thumb/How-does-quantum-tunneling-work-in-photosynthesis.pdf

1/ Chlorophyll absorption, especially in chlorophyll-protein complexes, is not null at 700 nm.

2/ Above all, photosystem 1 is still excited in this far-red zone, allowing the PS1+PS2 chain to work efficiently from water oxidation to NADP+ reduction (Emerson effect). This classical information can be found in all textbooks.

An interesting update:

Article Far-red photosynthesis: Two charge separation pathways exist...