Light analysis

[TyroneGenade]

There is a LOAD of data at http://www.apsa.co.za/board/index.php?topic=4454.0 with respect to spectra (T8, T5, LEDs) as well as PPF and PUR. These types of experiments are difficult to control as blue photons have different energy values compared to red photons. In fact light blue photons have different energy values to dark blue photons... As plant growth is a product of energy input being able to control energy input is very important to measuring how effective the light is as promoting photosynthesis. The ratios of red: blue light also seem to be important rather than absolute red or blue light.

In aquarium circles the Arcadia Plant Pro has a very good reputation. It also has a Red/blue ratio and PUR value very close to that of sunlight... The Osram Skywhite is also considered a good tube but has a poor R/B ratio but good PUR and PAR... I could go on but when you start looking at the "numbers" things get very confusing very quickly. What seems to matter is how much red and how much blue light is emitted by the tube when you want to pick a good tube.

LEDs square up very well with the photosynthetically useful spectrum and generally have good Red/Blue ratios and quantities emitted. All round, they seem to be the best bet.

With regards to "rate limiting steps" if you mean which enzymatic process limits photosynthesis then the answer is none of them. Rate limiting steps, in the sense of slowest enzymes limiting the entire process, don't exist in nature. So far, enzymes in their natural environment operate at at most 10% of their maximal rate due to substrate limitation (most operate at a 100th of the maximal rate). (Rate limiting steps are only seen in substrate saturated test tubes. Read David Fell's Understanding the control of metabolism.) It is the supply of substrate that limit metabolic flux. In the case of photosynthesis that is CO2, H2O but also ADP and NADP+. If the later runs out then the chlorophyll will keep producing electrons that are never accepted by NADP+ and instead can cause free radicals and leaf burn. At http://www.apsa.co.za/board/index.php?topic=4454.msg109062#msg109062 I posted data showing that photosynthetic flux levels off at about 1000 PPF and is most sensitive from 1 to 200 PPF. In another thread here someone provided data for Paphs in the wild and most of the PPF values were in this range. Within this range the plant will not be limited for substrate.

As 1 W of T8 or T5 light will produce about 1 PAR, it means that to get 200 PPF (PAR/m2/s) you would need about 200 W/m2. If you use the data in the first link you can equate your energy input from W to PPF or PUR etc... Using Lux meter APPs for cell phones you can use the Lux values to convert to PPF or PUR as well... Thanks for Cor De Witt (Greystoke on the above cited forum) you have all the data you need for some well constructed experiments.

Tyrone the Biochemist.

 

[DavidCampen]

There is a LOAD of data at http://www.apsa.co.za/board/index.php?topic=4454.0 with respect to spectra (T8, T5, LEDs) as well as PPF and PUR. These types of experiments are difficult to control as blue photons have different energy values compared to red photons. In fact light blue photons have different energy values to dark blue photons... As plant growth is a product of energy input being able to control energy input is very important to measuring how effective the light is as promoting photosynthesis.
...
As 1 W of T8 or T5 light will produce about 1 PAR, it means that to get 200 PPF (PAR/m2/s) you would need about 200 W/m2. Tyrone the Biochemist.

Actually, photosynthesis is a quantum effect, the energy from an absorbed blue photon of 450 nm produces no more carbon fixation that the energy from a red photon of 660 nm.

 

[TyroneGenade]

Thanks for the correction, David. I should have been more specific as I was referring to the difficulty of using the energy consumption of the lights to predict how many photons the light is going to emit of a particular energy (color), and therefore photosynthetic response. 1 W of red light gives many more photons than 1 W of blue light. As the different lamps have different spectra, and as the photosystems and chlorophylls have different light absorptive properties, it is difficult to draw conclusions if only power input is controlled. One needs to know the PPF and PUR values.

 

[Bjorn]

If you check this one, you will find that also the green light is important...
http://www.heliospectra.com/sites/w...ents/what_light_do_plants_need_2012-10-05.pdf
and
http://pcp.oxfordjournals.org/content/50/4/684.full

 

[DavidCampen]

If you check this one, you will find that also the green light is important...
http://www.heliospectra.com/sites/w...ents/what_light_do_plants_need_2012-10-05.pdf

This is an excellent paper. The physics of photosynthesis is fascinating, for example, the paper briefly mentions Foerster Energy Resonance Transfer (actually it is Foerster Resonance Energy Transfer (FRET)). This process can be described as energy transfer via the emission and absorption of virtual photons.
http://en.wikipedia.org/wiki/Förster_resonance_energy_transfer

 

[TyroneGenade]

Very interesting. We, in the aquarium hobby, have known for a long time that the green light was important. The tubes with the best plant growth reputations tend to be tri-chromatic tubes with blue, green and red peaks. For shade-loving plants, green light is probably important as most of the red and blue has been absorbed by the canopy above... But then we look at the actual data shown in the first posts of the this thread and the Paphs clearly like the red/blue heavy lighting. Osram Fluora has almost no green light in it... Plant and lighting needs are probably species specific...

An important experiment, perhaps, is to grow the Paph under 6500 K (trichromatic) light for a few weeks and then measure photosynthetic response. Has the plant adapted to the light?

 

[ALToronto]

An important experiment, perhaps, is to grow the Paph under 6500 K (trichromatic) light for a few weeks and then measure photosynthetic response. Has the plant adapted to the light?

You would have to measure it against paphs grown under red/blue light only, and see if the trichromatic light gives better results.

I was surprised to see how strong the green peak is in 'warm white' light (2700-3000K), both LED and fluorescent. I know growers who swear by their 3000K lights and insist that they give better growth than 'daylight' 6500K lights. I get the impression that trichromatic light is more of a shotgun approach - give the plants the full spectrum and let them take what they need from it. Some people have found that some plants only really need the red and blue wavelengths. That's fine if it works for them, but I'd hate to look at plants illuminated by those lights. So I like the shotgun approach, and the few extra dollars a year I would spend on unneeded wavelengths are more than worth it if the plants are a pleasure to look at.

 

[TyroneGenade]

The warm whites work well over fishtanks as well, but they don't look good. They have strong peaks at 610, 545 and 435 nm. 6500 K lamps have the same peaks but the 610 and 435 are about the same size, with a larger 545 peak.

Your idea of a controlled experiment is better than mine but I don't know how feasible it is given Polyantha's growing conditions which I why I suggested the simpler (less informative) experiment.

 

[naoki]

Very interesting. We, in the aquarium hobby, have known for a long time that the green light was important. The tubes with the best plant growth reputations tend to be tri-chromatic tubes with blue, green and red peaks. For shade-loving plants, green light is probably important as most of the red and blue has been absorbed by the canopy above... But then we look at the actual data shown in the first posts of the this thread and the Paphs clearly like the red/blue heavy lighting. Osram Fluora has almost no green light in it... Plant and lighting needs are probably species specific...

An important experiment, perhaps, is to grow the Paph under 6500 K (trichromatic) light for a few weeks and then measure photosynthetic response. Has the plant adapted to the light?

The first article is summarizing PS well without being technical. Tyrone, some data showed that green is important in the high light plants (as indicated in the 2nd paper). I believe that this is related to sun vs shade leaf syndrome. Sunny leaves with intense light has more layers of photosynthetic cells (parenchyma) per leaf. So green light which goes into the deeper layer is beneficial. Shade plants generally has thinner leaves, but increase the surface area to receive every possible light. But within Paphs, this syndrome isn't completely applicable (because some species have to deal with drought where thicker leaves are better to reduce loss of water).

Also the action spectrum is mostly measured in crop plants which receive full sun (e.g McCree 1972, whose data were used for the paper linked by Bjorn). It would be interesting to see how different the spectra of shade plants are.

With the planted aquarium, I also use a bit bluer light (6500k). In theory, bluer light should reduce the etiolation/elongation of stems, and I don't want to trim the stem plants too frequently. I don't know if this is the case with aquatic plants, though (the spectra under water become bluer as the depth increase, right?).

 

[Rick]

But within Paphs, this syndrome isn't completely applicable (because some species have to deal with drought where thicker leaves are better to reduce loss of water).

Drought for Paphs is a relative term and thick leave correltations haven't held up well for water conservation in paphs. The total annual rainfall for the habitat of Mexipedium is about the same as Middle TN, so not what I would call truly xeric drought conditions.

A study done on a thick and thin leafed paph species (albeit in a GH) showed they were both C3 heavy water consumers (no CAM capability).

At this time I don't think a CAM slipper has been determined although I doubt that anyone has tested Mexipedium or the Brachypetalum.

 

[naoki]

The emission spectrum of the heliospectra's grow light is pretty interesting:
http://www.heliospectra.com/products-solutions/l4a-s20
Really wide band. I wonder what 850nm is for. Pfr (phytochrome) absorption peak is around 740-750nm, so it is well beyond that. The other model (L4a-S10) which they have is more conventional (red dominated with FR).

 

[naoki]

Drought for Paphs is a relative term and thick leave correltations haven't held up well for water conservation in paphs. The total annual rainfall for the habitat of Mexipedium is about the same as Middle TN, so not what I would call truly xeric drought conditions.

A study done on a thick and thin leafed paph species (albeit in a GH) showed they were both C3 heavy water consumers (no CAM capability).

At this time I don't think a CAM slipper has been determined although I doubt that anyone has tested Mexipedium or the Brachypetalum.

Rick, you are right, it's unlikely to find a CAM slipper. I think that one of the paper used a Brachy to show it is likely to be C3 (or was it P. parishii?), because they suspected that within papahs, those thicker leaved ones would be more likely to be CAM.

But aside from CAM, we think there is a general sunny-shade leaf syndrome (well according to basic textbooks). One phenomenon implicit in this is that high light is correlated with heat (and water usage). Thicker leaves reduce the (surface area)/(leaf volume), a factor which can contribute to water use efficiency (WUE). Some paphs are more epiphytes/lithophytes than other paphs, so this could influence the leaf syndrome, too. Also, aren't northern species (e.g. P. armeniacum) has to go through drier winter?

 

[TyroneGenade]

With the planted aquarium, I also use a bit bluer light (6500k). In theory, bluer light should reduce the etiolation/elongation of stems, and I don't want to trim the stem plants too frequently. I don't know if this is the case with aquatic plants, though (the spectra under water become bluer as the depth increase, right?).

The stem elongation has to do with far red light, best I recall. Osram Fluora and Sylvania Gro-lux both emit a lot of light in the 650 to 700 nm range which would cause stem elongation. This far red light could be what is causing Polyantha's plant to begin photosynthesing sooner than the other tubes. Most pictures I see proclaiming the growth promoting effects of "plant lamps" generally show long, lanky plants... As far as biomass is concerned you probably get more biomass on full spectrum light.

I think plants are very adaptive. They can modify their photosensitive pigment ratio to use what light is available. The PAR spectrum I normally see referenced is for a water plant... I have seen some PAR spectra of algae and they are very different.

 

[naoki]

The stem elongation has to do with far red light, best I recall. Osram Fluora and Sylvania Gro-lux both emit a lot of light in the 650 to 700 nm range which would cause stem elongation. This far red light could be what is causing Polyantha's plant to begin photosynthesing sooner than the other tubes. Most pictures I see proclaiming the growth promoting effects of "plant lamps" generally show long, lanky plants... As far as biomass is concerned you probably get more biomass on full spectrum light.

I think plants are very adaptive. They can modify their photosensitive pigment ratio to use what light is available. The PAR spectrum I normally see referenced is for a water plant... I have seen some PAR spectra of algae and they are very different.

I think stem elongation and leaf expansion are influenced by both red (phytochrome) and blue (cryptochrome). Check the 2nd and 3rd para of the intro here: http://cpl.usu.edu/files/publications/poster/pub__2576523.pdf
Also, the photos show the influence of light on photomorphogenesis, but it's in a high light plant.

I think the idea of NASA-related LED stuff was that they started with red light (most efficient), but they added a bit of blue to reduce the elongation.

I'm not familiar with FR causing PS sooner. Is it right? I know that blue light stimulate the stomata opening (needed in C3 plants for efficient C assimilation) most (and green light reverse the reaction). Paphs are used for this type of research because they are unique (the guard cells don't contain chloloplast). Even without chloroplast, blue light stimulates Paph stomata opening most.

You are right about algae, the first link by Bjorn also mentioned the different action spectra for algae. Some (but not all) algae have different chlorophyll (a and c, I believe).

 

[Rick]

Rick, you are right, it's unlikely to find a CAM slipper. I think that one of the paper used a Brachy to show it is likely to be C3 (or was it P. parishii?), because they suspected that within papahs, those thicker leaved ones would be more likely to be CAM.

But aside from CAM, we think there is a general sunny-shade leaf syndrome (well according to basic textbooks). One phenomenon implicit in this is that high light is correlated with heat (and water usage). Thicker leaves reduce the (surface area)/(leaf volume), a factor which can contribute to water use efficiency (WUE). Some paphs are more epiphytes/lithophytes than other paphs, so this could influence the leaf syndrome, too. Also, aren't northern species (e.g. P. armeniacum) has to go through drier winter?

One paper I recall for a "thick leaved slipper" used parrishii. Which does have thick leaves, but comes from a more consistently wet/cooler place than say niveum. Also the cool/drier winters for the northern species may not have rainfall, but lots of fog, dew and even frost.

The generalization with leaf structure and water balance is probably a lot more complex. Don't forget to add in root water storage too. But for a more side by side comparison compare exul leaves to niveum or godefroyae leaves which are found within a few feet of each other on those blistering Krabi islands.

When looking at leaf structures and water use strategies, probably need to get more extreme and look at whole plant structures (like comparing a an epiphytic bulbophylum to a sympatric aboreal paph).

Bulbo small plant with thick leaf + psedobulb + thin roots. P parishii huge plant with thick leaves and thick roots.????? Or look backwards into plant structures that are known CAM and compare to the whole plant strategies of the C3's.

If you compare something like Cattleya schilleriana or "mule ear" oncidia leaves to even the thickest toughest paph leaves, its a whole 'nother world.

 

[naoki]

I agree; the syndrome is just a general trend (useful for teaching the basic plant biology), and individual cases are more complicated. All environmental (both biotic and abiotic) become important to determine the adaptive morphology. Also as you point out, there is phylogenetic and morphological constraints.

Going back to the green light, it is possible that they are useful for some thick leaved paphs or paphs growing under direct sun. But the enhancing effect of green light may be fairly weak for most paphs. Green light is used for photosynthesis for sure, but red light is probably more efficient for paphs (unless you grow them in intense light). From my understanding, the green light start to become more effective than red light, once the top layers of cells are saturated for PS by intense light.

 

[lepetitmartien]

The emission spectrum of the heliospectra's grow light is pretty interesting:
http://www.heliospectra.com/products-solutions/l4a-s20
Really wide band. I wonder what 850nm is for. Pfr (phytochrome) absorption peak is around 740-750nm, so it is well beyond that. The other model (L4a-S10) which they have is more conventional (red dominated with FR).

There's UVA, I wouldn't go under this one.

I don't understand their spectrum…

Their LA4 s10 is aimed at labs who want a versatile customizable light source.