PAR...how is it weighted? and other ??'s

[JCTewks]

I'm starting this thread as a continuation of a discussion that can be found here .

The questions are:

1.) What is the TRUE definition of PAR?

2.) How is PAR weighted in the spectrum...is the scale linear, weighted heavier in the shorter wavelengths, or does it follow a spectral curve similiar to the response of chlorophyll?

3.) Please confirm or refute this statement

The ONLY reason that the 100w 600nm bulb would have more available radiation than the 100w 420nm bulb is that it is easier for a bulb to produce the higher wavelengths...hence why a 20K MH will have less PAR than a 10K. The PAR difference has niothing to do with spectrum, only how effectively a bulb can produce blue.

4.) How/Why is it that most bulbs of higher PAR are "yellower" bulbs, while the "bluer" bulbs PAR is considerably lower for the same amount of power put into the bulb?

 

[greenbean36191]

1. Par is simply the number of photons in the range from 400-700 nm.
2. It's not weighted. 1 photon of red light is exactly equal to 1 photon of blue light, green light, yellow light, orange light, etc. It doesn't follow an activity spectrum of any pigment and trying to weight it like this would limit it's utility since in the real world, almost all autotrophic organisms use a mixture of pigments and this varies from species to species, and even within individuals over time.

3. I'm not really sure I'm understanding the last sentence, but the rest seems to be correct. It takes more energy to emit of photon of higher wavelength, so fewer are emitted per unit of energy input, therefore you get a lower PAR since it's just a photon count.

4.^

 

[Philwd]

3. I'm not really sure I'm understanding the last sentence, but the rest seems to be correct. It takes more energy to emit of photon of higher wavelength, so fewer are emitted per unit of energy input, therefore you get a lower PAR since it's just a photon count.

Did you mean shorter wavelength and higher Kelvin rating as blue and UV (i.e. higher energy photons) are shorter wavelengths?

 

[greenbean36191]

Doh, I said it backwards. Good catch.

It should say:
"It takes more energy to emit of photon of shorter wavelength, so fewer are emitted per unit of energy input, therefore you get a lower PAR since it's just a photon count.

 

[BeanAnimal]

When in doubt about "energy levels" and the color spectrum, just remember what you know about FIRE.

The inner area near the source of the flame (high energy) is BLUE. The part of a flame that is farthest from the source (lower energy) is fairly RED.

It is no coincidence that we rate the color rendering of a bulb in Kelvins! The different COLOR areas of the flame MATCH the Kelvin temperatures on the Kelvin scale.... all of course because William Kelvin heated carbon to different temperatures and recorded its COLOR!

If none of that rings a bell from 8th grade science class... then just remember ROY G. BIV

RED
ORANGE
YELLOW
GREEN
BLUE
INDIGO
VIOLET

Lowe energy to high energy....

Now if we think about it for a moment, we can understand why (in general) BLUE bulbs have LESS PAR then YELLOW bulbs per Watt of power input. The same reason that MOST of a match burns Red, then yellow with very little blue. Most of the energy released during burning is in the lower energy part of the reaction. There is little left that makes it to the higher energy state (temperature). Simply put, higher temperatures are harder to achieve than lower temperatures. Furthermore, to get to a higher temperature (energy) the reaction MUST pass through the lower temperature (energy) state. I.E. You can't get ANY blue flame without having some RED flame, but you can have a LOT of RED flame with little or no BLUE flame.

Hope that helps.

 

[shelburn61]

nevermind

 

[hahnmeister]

With bulbs though, you can have lots of blue and no red though. Blue light takes more energy to produce because its higher in frequency (shorter wavelength) than red.

But phosphor based bulbs... if you remove their phosphors and just have a clear bulb, are UV-C lamps. With many phosphor bulbs, they still make more light if they are warmer and those are easier to make, but because they have to go through the conversion of energy from UV, they tend not to be as good at making those warmer spectrums as halides. They do a rather good job at making blue though. And LED's... well, they tend to be better at making blue than anything else.

 

[MCsaxmaster]

+1 for what Mike said.

1) PAR = photosynthetically active radiation. It's the number of "photosynthetically active" photons (that is, those with wavelength 400-700 nm) that hit a surface per unit time. The units are typically umol photons/m2/s.

2) It's not weighted for spectrum. The number of photons hitting the surface are counted. Wavelength is irrelevant. This is particularly applicable to light intensity measurments for photosynthetic organisms because of the way in which photosynthesis works. Any photon that is absorbed and used in photochemistry, regardless of the original wavelength of that photon, yields exactly the same amount of work. An absorbed blue photon is exactly equivalent to a green or red photon in terms of what photosynthesis can actually do with it, hence why we want to count photons for this measure.

3) Agreed, the statement isn't terribly clear.

4) Ultimately it has to do with the properties of the gases, halides, etc. that are mixed in the bulb. Different mixes will give different quantities and qualities (= spectra) of light. As for why the mixes that give very "blue" looking spectra tend to produce less light than other mixes that produce somewhat more "whiteish" spectra, I don't know.

Chris

 

[pjf]

<a href=showthread.php?s=&postid=13256456#post13256456 target=_blank>Originally posted</a> by MCsaxmaster
Any photon that is absorbed and used in photochemistry, regardless of the original wavelength of that photon, yields exactly the same amount of work. An absorbed blue photon is exactly equivalent to a green or red photon in terms of what photosynthesis can actually do with it, hence why we want to count photons for this measure.

Does this apply to photons absorbed by "helper" pigments?

 

[hahnmeister]

Thats not exactly true. Pigments filter out different frequencies depending on the coral. Im not saying it has to do with energy conversion of those light frequencies, but more to do with how the coral blocks them out. But it has been found that certain frequencies can cause photoinhibition in a coral easier than others... like actinic, UV-A, etc.

 

[MCsaxmaster]

Any photon that is absorbed and used in photochemistry, regardless of the original wavelength of that photon, yields exactly the same amount of work. An absorbed blue photon is exactly equivalent to a green or red photon in terms of what photosynthesis can actually do with it, hence why we want to count photons for this measure.

<a href=showthread.php?s=&postid=13293174#post13293174 target=_blank>Originally posted</a> by pjf
Does this apply to photons absorbed by "helper" pigments?

The short answer is yes...

...but let me explain just a bit.

Photons are used by photosystem II to move electrons down an e- transport chain. In order to move an electron, it takes a particular quanta of energy. That amount of energy corresponds roughly to a red photon. Hence, whether a blue photon, green photon, red photon, etc. is absorbed, only the energy equivalent to a red photon is actually used as part of photosynthesis. If there is excess energy in an absorbed photon (e.g., a blue photon is more energetic than a green is more energetic than a red photon) that excess energy is lost to fluorescence or heat. So whichever pigment absorbs a given photon is immaterial in terms of how that photon can be used by photochemistry.

BUT, in order to get to the point of actually being used in photochemistry, the energy in a photon has to be transported down an e- transport chain to a reaction center of PSII. Typically this means that the photons are harvested by antenna proteins containing any of the photopigments (including secondary pigments) used by the organism. While these energy transfers are typically very efficient, no transfer of energy is ever 100% efficient. Hence, the energy from absorbed photons is sometimes lost along the way, never makes it to a reaction center, and hence can never be used in photochemistry (lost instead as fluorescence or heat). For the overall process, healthy, happy dinoflagellates typically have a quantum efficiency (= yield) of ~0.6, meaning 60% of the absorbed photons actually get used in photochemistry. The difference between absorbing a photon in an antenna protein with peridinin vs. chl c2 vs. ch a, however, is negligible, and probably immeasurable.

Chris

 

[MCsaxmaster]

<a href=showthread.php?s=&postid=13293245#post13293245 target=_blank>Originally posted</a> by hahnmeister
Thats not exactly true. Pigments filter out different frequencies depending on the coral. Im not saying it has to do with energy conversion of those light frequencies, but more to do with how the coral blocks them out. But it has been found that certain frequencies can cause photoinhibition in a coral easier than others... like actinic, UV-A, etc.

Hmmm, I'm not entirely sure what you're driving at here. The effects of UV on the photosynthetic apparatus are not related to photosynthesis, but rather physical damage of PS II by excessively energetic photons. UV goes in and starts busting things up

 

[shelburn61]

Great thread! Answers many longstanding questions for me.

<a href=showthread.php?s=&postid=13256456#post13256456 target=_blank>Originally posted</a> by MCsaxmaster
Wavelength is irrelevant. This is particularly applicable to light intensity measurments for photosynthetic organisms because of the way in which photosynthesis works. Any photon that is absorbed and used in photochemistry, regardless of the original wavelength of that photon, yields exactly the same amount of work. An absorbed blue photon is exactly equivalent to a green or red photon in terms of what photosynthesis can actually do with it, hence why we want to count photons for this measure.
Chris

How applicable is this statement to production of visible pigments in corals? If the goal is to induce production of the proteins responsible for the bright colors in acros, should we just focus on raw PAR or does spectrum then become more important?

 

[MCsaxmaster]

<a href=showthread.php?s=&postid=13296005#post13296005 target=_blank>Originally posted</a> by shelburn61
Great thread! Answers many longstanding questions for me.

How applicable is this statement to production of visible pigments in corals? If the goal is to induce production of the proteins responsible for the bright colors in acros, should we just focus on raw PAR or does spectrum then become more important?

That's a very good question, and one I'm not sure there is as yet a clear answer to (simply for lack of data, not for sake of the difficulty in getting the numbers), but I think we can do some educated speculation.

First, the production of some coral pigments (keep in mind these are coral pigments, not photosynthetic pigments) does seem to be upregulated or downregulated based on light intensity. Others seem to be expressed or not expressed regardless of light intensity (i.e., different light regimes don't seem to have any effect on pigment production). For those pigments that are expressed or not expressed regardless of light intensity (e.g., GFP in many corals, some other pigments as well) clearly it doesn't much matter which lighting we choose. For those that do respond to light intensity, pretty well across the board their production is upregulated in response to higher light intensity.

I can think of two logically feasible ways in which light spectrum could play a role in regulating pigment production.

1) The action spectra of zooxanthellae tend have broad peaks in the cyan to violet (~400-500 nm) and again in the red/orange (~670-700 nm) though they absorb at all visible wavelengths. If the absorption efficiency in the blue, for example, were much, much higher than in the rest of the spectrum AND the production of coral pigments were directly related to the number of photons absorbed by PS II, then spectrum could matter. In this case, significantly more blue photons would be absorbed by PS II than green yielding more pigment production.

However, while the absorption efficiency is higher in the blue than in the green, it typically isn't THAT much higher for most corals. In addition, we don't know the cue used by corals to upregulate or downregulate pigment production. There is a correlation between light intensity and pigment production, but what exactly does that mean?

2) The corals might not be taking signals from the zooxanthellae directly and instead may be sensing light intensity themselves and responding accordingly. If the photoreceptors the corals would be using to do that are more sensitive to particular wavelengths (e.g., blue vs. green) then by providing a lot of that wavelength, we might be able to "fool" the corals into producing the pigments under lower light intensity than they normally would.

The article published in Advanced Aquarist where corals were grown under blue lighting and white lighting of the same intensity and ended up looking the same (i.e., no obvisous visual difference in pigments) suggests to me that this mechanism probably isn't viable.

Hence, I think the most likely scenario is that spectrum really just doesn't matter much or not at all and intensity is really what counts. However, unless we have some hard numbers, there's no way to be too confident in any position.

Chris

 

[pjf]

<a href=showthread.php?s=&postid=13295196#post13295196 target=_blank>Originally posted</a> by MCsaxmaster
The difference between absorbing a photon in an antenna protein with peridinin vs. chl c2 vs. ch a, however, is negligible, and probably immeasurable.

Does this mean that a green photon absorbed by peridinin produces as much carbohydrates as a red photon absorbed by chlorophyll-a?

 

[Philwd]

Interesting Chris. If what you say is true about spectrum why do many bulbs heavy in blue have washed out reds?

 

[hahnmeister]

<a href=showthread.php?s=&postid=13295210#post13295210 target=_blank>Originally posted</a> by MCsaxmaster
Hmmm, I'm not entirely sure what you're driving at here. The effects of UV on the photosynthetic apparatus are not related to photosynthesis, but rather physical damage of PS II by excessively energetic photons. UV goes in and starts busting things up

Many corals can use UV-A. But they are more sensitive to lower levels of it because it does contain more energy. Dana Riddle is the one, I believe, who has come up with the research on how bluer spectrums can cause photoinhibition easier than warmer ones... so it would seem that there is something to the varying levels of energy coming from the light source's various frequencies... like I said... nothing to do with energy conversion in the coral, but still of concern. Light levels for many corals are much more than they need for their daily carbon intake, much of that light energy just being shed in their slime... so the importance of 'too much' or 'too little' with regards to energy conversion is of very little importance compared to 'how they handle' all that light.

 

[MCsaxmaster]

<a href=showthread.php?s=&postid=13305682#post13305682 target=_blank>Originally posted</a> by pjf
Does this mean that a green photon absorbed by peridinin produces as much carbohydrates as a red photon absorbed by chlorophyll-a?

Pretty much, yes. The efficiency of energy transfer through the antenna proteins is pretty high. Once absorbed, all photons have about equal potential of being used in photochemistry (~60% for healthy, happy dinoflagellates at lower light intensities).

<a href=showthread.php?s=&postid=13311035#post13311035 target=_blank>Originally posted</a> by Philwd
Interesting Chris. If what you say is true about spectrum why do many bulbs heavy in blue have washed out reds?

Because whatever mix of gases, halides, etc. in those bulbs produces a lot of light near ~450 nm, and very little elsewhere. Beyond that, I have no idea

<a href=showthread.php?s=&postid=13312368#post13312368 target=_blank>Originally posted</a> by hahnmeister
Many corals can use UV-A. But they are more sensitive to lower levels of it because it does contain more energy.

Only very near UV can be absorbed by photopigments for photosysnthesis to any significant degree though. Usually it is UV-B we’re concerned with in terms of photonhibition. UV-B is absorbed well by proteins though (and nucleotides), hence it damages the physical structure of PSII, causing photoinhibition.

<a href=showthread.php?s=&postid=13312368#post13312368 target=_blank>Originally posted</a> by hahnmeister
Dana Riddle is the one, I believe, who has come up with the research on how bluer spectrums can cause photoinhibition easier than warmer ones... so it would seem that there is something to the varying levels of energy coming from the light source's various frequencies... like I said... nothing to do with energy conversion in the coral, but still of concern.

Hmmm, I’m not so sure about that. Could I see those data?

<a href=showthread.php?s=&postid=13312368#post13312368 target=_blank>Originally posted</a> by hahnmeister
Light levels for many corals are much more than they need for their daily carbon intake, much of that light energy just being shed in their slime... so the importance of 'too much' or 'too little' with regards to energy conversion is of very little importance compared to 'how they handle' all that light.

Hmmm, could you clarify a bit what you mean here? Most corals in shallow water experience dynamic photoinhibition during the middle hours of the day, saturating intensities for several hours, and undersaturating intensities for a few hours (at least on the outer, unshaded surfacesâ€"the story is very different within branching colonies). That’s a result of light intensity varying by many orders of magnitude over the course of a day due to movement of the sun. In captivity, where we have static light intensity, we have a very different situation. Under constant light intensity, rates of photosynthesis are constant in corals under otherwise normal conditions.

Also, I wouldn’t disregard the loss of photosynthate in coral mucus. They lose a lot of nitrogen in that mucus too. Clearly, whatever they are doing with all that mucus, it serves very important functions for them.

Chris

 

[hahnmeister]

As for the data on blue light (UV-A in particular), you would have to ask Dana I believe. It came up in conversation/emails with him.

Althouth light intensity in nature varies throughout the day and rarely does in captivity, the total amount of light absorbed as far as the coral is concerned is the same... that is why total exposure throughout the day, if constantly varying or not, is simply summed up... much like charging a battery. So all you do is sum up every second of light intensity and add it to the total just the same. Without getting into the integral calc, lets say you had a coral that gets a peak intensity of 1000 at noon (or shortly after), and less and less as you go either forward or back in time until 6am or pm. This total per hour may average out to say... 300 micromol/m2/s... and if you have that coral under light that is 300 for 12 hours a day... the photosynthetic response would be just the same, as its really just storing up for its night cycle to actually process that carbon. Likewise, if you had light levels of 400 for 9 hours a day, it would get just as much. The pigments would no doubt respond differently to protect the coral from the different peak levels of intensity, but otherwise its just 'charging the batteries'. This buildup of carbon is nitrogen limited though, and so most corals just shed their excess carbon in the form of slime because they are nitrogen limited (a coral that gets 160% of its daily carbon from light will shed 60% through slime production because it cant store the rest until the next day). Tom Wyatt and Borneman were talking about it all weekend with their lectures on coral nutrition and coral chemistry (internal chemistry pathways more like it). I believe those lecture notes will be posted. But corals are nitrogen limited, and so simply blasting them with more and more light does little. You want to really boost growth? Provide more flow and feed like mad. Borneman's lecture was interesting, and Tom referenced it several times since they were related and had many parallels. We dont feed nearly as much or as well as we should.

But as far as the 'mucus', Tom's talk mentioned that it may be for protection, but mostly to shed the coral's excess energy in the case of excess light (suggesting that many corals get too much light and that is how they shed that energy). Also, that the stony skeleton isnt so much an evolutionary adaptation for structure, but that the formation of calcium around the polyps is more for food storage, since the carbonate can be converted back to a carbon source.

 

[MCsaxmaster]

<a href=showthread.php?s=&postid=13318204#post13318204 target=_blank>Originally posted</a> by hahnmeister
As for the data on blue light (UV-A in particular), you would have to ask Dana I believe. It came up in conversation/emails with him.

Hmmm, but UV-A isn’t blue light. It’s invisible to us, hence it has no color. However, it is nearest deep violet, not blue. Again though, I’d have to see the data to entertain the notion that blue light causes measurably more photoinhibition in corals than red or green of the same intensity.

<a href=showthread.php?s=&postid=13318204#post13318204 target=_blank>Originally posted</a> by hahnmeister
Althouth light intensity in nature varies throughout the day and rarely does in captivity, the total amount of light absorbed as far as the coral is concerned is the same... that is why total exposure throughout the day, if constantly varying or not, is simply summed up... much like charging a battery. So all you do is sum up every second of light intensity and add it to the total just the same. Without getting into the integral calc, lets say you had a coral that gets a peak intensity of 1000 at noon (or shortly after), and less and less as you go either forward or back in time until 6am or pm. This total per hour may average out to say... 300 micromol/m2/s... and if you have that coral under light that is 300 for 12 hours a day...

Nnnnoo, no no, that’s not how photosynthesis works. That would only work if the organism were at low light intensity (subsaturating) for the entire day. The photosynthetic response under a naturally varying light cycle due to solar precession is not the same as it is under constant light intensity. A coral exposed to 12 hrs of light at 300 umol photons/m2/s would probably be near the point of photosaturation, but for most corals wouldn’t be getting nearly enough light to cause significant photoinhibition. A coral exposed to a max intensity of 1000 umol photons/m2/s is going to be photoinhibited during that day. During the early morning and late evening it will be well undersaturated with light. NPP, GPP, photodamage, etc. will all be different between these scenarios.

<a href=showthread.php?s=&postid=13318204#post13318204 target=_blank>Originally posted</a> by hahnmeister
the photosynthetic response would be just the same, as its really just storing up for its night cycle to actually process that carbon.

Huh? What do you mean waiting for the night cycle to process the carbon? Why would they wait for night to utilize the carbon they’ve fixed?

<a href=showthread.php?s=&postid=13318204#post13318204 target=_blank>Originally posted</a> by hahnmeister
Likewise, if you had light levels of 400 for 9 hours a day, it would get just as much.

Think about that though: you’re saying that production (e.g., NPP) is governed simply by the number of photons the corals are exposed to per day. So, at 300 umol photons/m2/s X 3600 s/hr X 12 hrs/day = 12.96 mol photons/m2/day. If we ramp up the intensity substantially and adjust down the photoperiod we can get the same number of photons hitting the corals with intensity of 3000 umol photons/m2/s for 1.2 hrs. If we expose the corals to light intensity 150% the intensity of unfiltered sun, do you think they’re going to do well? We can easily get that sort of light technology out of specialty bulbs, should we be doing that? No, were we to try that, the corals would fry during those 1.2 hrs.

<a href=showthread.php?s=&postid=13318204#post13318204 target=_blank>Originally posted</a> by hahnmeister
The pigments would no doubt respond differently to protect the coral from the different peak levels of intensity, but otherwise its just 'charging the batteries'.

No, that’s not how photosynthesis works.

<a href=showthread.php?s=&postid=13318204#post13318204 target=_blank>Originally posted</a> by hahnmeister
This buildup of carbon is nitrogen limited though, and so most corals just shed their excess carbon in the form of slime because they are nitrogen limited (a coral that gets 160% of its daily carbon from light will shed 60% through slime production because it cant store the rest until the next day).

Nnnooo, carbon fixation is only N-limited to the extent that N-limitation could reduce the production of photosynthetic reaction centers and/or associated proteins. Corals lose a lot of photosynthetically fixed carbon in mucus, but that’s no reason to think that they are using mucus production simply as a mechanism to dump excess fixed carbon. They lose a lot of fixed carbon to gametes too. Should we suggest that gamete production is a means to simply purge excess carbon?

In addition, corals tend to eat a fair amount in nature. Counting photosynthetically fixed carbon AND carbon intake from feeding, most corals are getting 200-300% of their daily metabolic expenditure worth of energy per day. Of that 200-300%, 100% goes to metabolism, about 50-100% goes to mucus production, and the rest goes to gametet production, growth, defense, tissue repair, etc.

Why wouldn’t they be able to store that fixed carbon until the next day?

<a href=showthread.php?s=&postid=13318204#post13318204 target=_blank>Originally posted</a> by hahnmeister
Tom Wyatt and Borneman were talking about it all weekend with their lectures on coral nutrition and coral chemistry (internal chemistry pathways more like it). I believe those lecture notes will be posted. But corals are nitrogen limited, and so simply blasting them with more and more light does little. You want to really boost growth? Provide more flow and feed like mad. Borneman's lecture was interesting, and Tom referenced it several times since they were related and had many parallels. We dont feed nearly as much or as well as we should.

Blasting them with more light does little good IF they are already photosaturated. Corals that grow at depth where light availability is low grow much, much more slowly than those in shallow water. It’s not an either or sort of thing though: corals that receive ample light, food, etc. grow fast. Those that don’t…don’t. I’d be the first to agree that most corals are woefully underfed in captivity though.

<a href=showthread.php?s=&postid=13318204#post13318204 target=_blank>Originally posted</a> by hahnmeister
But as far as the 'mucus', Tom's talk mentioned that it may be for protection, but mostly to shed the coral's excess energy in the case of excess light (suggesting that many corals get too much light and that is how they shed that energy).

1) What would be the purpose of wasting huge amounts of energy-rich food?

2) Where’s the evidence? Corals lose a lot of N in their mucus too, not just C. If mucus production is a mechanism for dumping excess fixed carbon, then why is their so much investment in it in terms of N, specialized proteins, etc.?

<a href=showthread.php?s=&postid=13318204#post13318204 target=_blank>Originally posted</a> by hahnmeister
Also, that the stony skeleton isnt so much an evolutionary adaptation for structure, but that the formation of calcium around the polyps is more for food storage, since the carbonate can be converted back to a carbon source.

Oh reaaally? Well, since my MS deals heavily with skeletogenesis in corals, I’d be very interested to hear how or why the skeleton is used as a repository for inorganic carbon

Chris