Man I just ran across this :
This is a must read with all the links included. Once we're done reading (myself included), then we can continue this debate. I just found out I know nothing.
Keep it bright!
Okay need to switch gears in mah brain xD. Well first; don't get all freaked out that and that all you know is wrong. I believe the guy gets a bit off with some things about spectrum. Otherwise there's a ton of nice links there and a good find!!
His primary basis is from a paper he links and he states --- "green is more photosynthetically efficient than red (pdf file). All the latest research and my own experiments back this claim"
First and foremost this paper is looking at light levels at or photoinhibition / saturation; when several active plant responses (both long-term and short) are also in place to avert damage. At high intensities, electron transport rate and CO2 fixation is reduced significantly in PSI and PSII photosystems. I guess I have a paper with a good pic to represent this.
In the paper he is going off of, it is stated;
" Because green light can penetrate further into the leaf than red or blue light, in strong white light, any additional green light absorbed by the lower chloroplasts would increase leaf photosynthesis to a greater extent than would additional red or blue light."
Here, in a high light scenario at capacity.......additional light supplied in green is Then more effective than additional blue or red.
Then the paper also states:
"On an absorbed quantum basis, the efficiency or photosynthetic quantum yield of green light is comparable with that of red light, and greater than that of blue light."
I'm sure you are aware of Action spectrum, Absorption spectrum and Quantum Yield and that's all they are referring to specifically here. If we look at the chart established and referred in the paper we can see this.
You can see that @ 550nm green does have a higher quantum yield than blue and not much less than red.
The paper also focuses on internal light levels and activities where it states;
"Using the method of Takahashi et al. (1994) , Vogelmann and Evans (2002) and Evans and Vogelmann (2003) indicated that, on a unit chlorophyll basis, the chloroplasts in the lowermost part absorb about 10 and <20%, respectively, of the green light of those in the uppermost part. For wavelengths with strong absorption, such as red and blue, the fractions are much smaller. In C. japonica, the absorption of 680 nm (red) light by the lowermost chloroplasts is <2% of the absorption by the uppermost chloroplasts on a unit chlorophyll basis. For blue light in spinach, the estimated absorption by the lowermost chloroplasts was <5% of that of the uppermost"
So, deep inside the leaf. Green is significantly higher in absorption vs other colors as the other colors have been previously absorbed.
They also talk quite a bit about photoinhibition and rubisco response w/ green light. Of note here they state:
"The greatest decrease in Fv/Fm in the uppermost part of the leaf was observed with blue light, and Fv/Fm approached high levels at depth. The second greatest damage to the surface chloroplasts was observed with red light, but the damage was confined to the irradiated half of the leaf. On the other hand, damage to the surface chloroplasts was least with green light, but continued deep into the leaf, probably because sufficient green light penetrated and was absorbed by the chloroplasts in the abaxial side."
.......
"As Nishio (2000) clearly postulated, and as we have detailed so far, red or blue light is preferentially absorbed by the chloroplasts in the upper part of the leaf. Then, when PPFD is high, the energy of these wavelengths tends to be dissipated as heat by the upper chloroplasts, while green light drives photosynthesis in the lower chloroplasts that are not light saturated."
......
"Namely, red light is more effective than green light in white light at low PPFDs, but as PPFD increases, light energy absorbed by the uppermost chloroplasts tends to be dissipated as heat, while penetrating green light increases photosynthesis by exciting chloroplasts located deep in the mesophyll. Thus, for leaves, it could be adaptive to use chlorophylls as photosynthetic pigments, because, by having chlorophyll with a ‘green window’ the leaves are able to maintain high quantum yields for the whole leaf in both weak and strong light conditions.
.....
Given these constraints, it would be ideal to have chlorophyll that enables considerable light absorptance, due to the high absorptivity of blue and red light, but also penetration of green light to the lower chloroplasts. As Nishio (2000) argued, this may explain why land plants adopted Chl a and b from green algae but did not develop other pigment systems.
and last with the paper;
"The most efficient situation is realized when the profile of light absorption and the profi le of photosynthetic capacity are perfectly matched, and all the chloroplasts in the leaf behave synchronously with respect to photosynthetic light saturation ( Farquhar 1989 , Terashima and Hikosaka 1995 , Richter and Fukshansky 1998 ). "
That paper is pretty good that he provided and does cover a lot of aspects. However, I think he brings this up "out of context" to some degree. To me this furthers the idea of plants being (and have evolved) adaptable to many situations. Also, with this information; various reasons as to "Why" can be drawn together easily. If we take a look a sunlight spectrum from a "farther distance"; some things can become apparent too.
Here we can see that throughout the entire spectrum of sunlight; plants adapted to the area with the highest percentage of energy (irrespective of visibility to us). Also, that the peak of this window is pretty much in the green band. It makes some sense then as to why plants may develop to be green and do not specifically peak in photosynthetic activity in these ranges (i.e. absorption spectrum). Nature doesn't take nature for granted (lol), so it also makes sense that; though not primarily deriving energy from green areas, the plant still can / does make use of this spectral band.
Next to this then we have red, which would be the most logical area for evolution as it has a lower energy state than blue; because of this, it can be absorbed in larger quantities without photoinhibition (heat, xanthophyll cycle, NPQ etc). Finally considering the blue end; this is the color typically most prevalent in low light (and underwater). It makes sense here that the plants would evolve an ability to specifically utilize the band for low light situations. Further it makes sense that the The xanthophylls / carotenoids would have their peaks in this region; not only from blue being the last remaining color in low light, but more importantly to ensure amino synthesis and photoprotection under the widest possible conditions.
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Before this I was of the opinion that full spectrum is always better than partial. When I had my fish store, we would throw an actinic on for color and otherwise a 6500K MH. All the research and hype in that industry leads you to 10-20,000K, but we always had better growth with 6500K . Before this too, my biggest hesitation with LED's as a primary light is related to their general lack of spectral diversity.
After reading this stuff. I'm of the same opinion xD. Just like with nutrients a balance is always the best option. Heck, really anything natural is all about balance.
sorry to ramble :)
