4 ms·

Why wouldn't fluctuations of sunlight that cause instability in the green spectrum also cause instabilities in the red and blue spectra?

uj8efdkjfdshf 6y ago
I think the point is that since the power available at these wavelengths vary sharply with frequency in these regions of the solar spectrum, the plant can easily compensate for brightness fluctuations in these portions of the spectrum with minor tweaks to the target wavelength of the relevant photosystems
- londons_explore 6y ago
  I'd this is the case, it's a shame the article didn't mention it. It makes sense the changing environmental conditions for a molecule could affect the wavelengths of light it absorbs (for example, pH, temperature, etc), but I'm not sure this has been demonstrated for plant pigments?
- Sniffnoy 6y ago
  I'm confused though -- how can the plant possibly vary this?
  - danbruc 6y ago
    In principle plants have several different variants of the light absorbing molecules with different absorption spectra but I don't know how this would actually be regulated. But it is certainly imaginable that plants vary the relative abundance of the different light absorbing molecules or their efficiencies and this could be more or less automatic because of varying conditions like pH or whatnot that affects efficiency or lifetime of the molecules with a simple feedback mechanism or it could be actively regulated by a more complex feedback loop.
floatrock 6y ago
> It might be highly efficient to specialize in collecting just the peak energy in green light, but that would be detrimental for plants because, when the sunlight flickered, the noise from the input signal would fluctuate too wildly for the complex to regulate the energy flow. > Instead, for a safe, steady energy output, the pigments of the photosystem had to be very finely tuned in a certain way. The pigments needed to absorb light at similar wavelengths to reduce the internal noise. But they also needed to absorb light at different rates to buffer against the external noise caused by swings in light intensity. The best light for the pigments to absorb, then, was in the steepest parts of the intensity curve for the solar spectrum — the red and blue parts of the spectrum. I admit there's a bit of a jump there (gotta read the actual article, not the journalist retelling I suppose), but I assume the gist of the math is something like this: Lets say direct green light delivers a maximum 100 "units of photo-energy" -- gonna play loose with the physics to demonstrate the math. When a cloud passes over it, lets say the intensity drops to only 75%. Lets also say for now we always convert the energy at 100% efficiency. So with green light, your 100 units of energy drops by 25 units with each passing cloud. Now lets say blue light delivers only 80 units of energy. When that same cloud passes over, 80 * 75% = 60 units of energy, or a drop of 20 units. So, if your process is sensitive to changes in absolute energy, you would rather have a swing of 20 units for every passing cloud than a swing of 25 units. Yeah, you might get less absolute energy (60 units rather than 75), but if the cost of energy swings in your process was very high, the tradeoff might be worth it. You could also play with the efficiency-of-conversion (ie have higher conversion efficiency at the lower-swing points) for some fun second-order effects. This is just a toy example of what the underlying dynamics could be. Gotta read the actual paper to understand the actual model they developed. https://arxiv.org/pdf/1912.12281.pdf https://arxiv.org/pdf/1912.12281.pdf
- wcoenen 6y ago
  > Now lets say blue light delivers only 80 units of energy. When that same cloud passes over, 80 * 75% = 60 units of energy, or a drop of 20 units. So, if your process is sensitive to changes in absolute energy, you would rather have a swing of 20 units for every passing cloud than a swing of 25 units. That's not exactly it. The idea is that the blue light absorption can be tuned (presumably by shifting the absorbed wavelengths by a few nanometer) to compensate for external changes. So if the overall light intensity drops 1%, the system responds by shifting the absorbed spectrum to get 1% more power. This only works in parts of the solar spectrum where power varies sufficiently versus wavelength, hence the preference for blue and red.
FriedPickles 6y ago
They do. The paper's point is that plants want to choose two wavelengths with different amounts of average power. This gives the plant a window to tune within to get the desired amount of output power. If the total illumination drops, the plant compensates by tuning more towards the high power wavelength, and vice versa. But the paper makes the point that the tuning mechanism isn't perfect due to internal noise. If the power level difference between the two input wavelengths is too great, then the random fluctuation of the tuning mechanism will itself create a lot of noise in the output. So basically there's an optimal value for the difference of average power between the two wavelengths. Now, why the plant doesn't absorb the peak green wavelength and the closest wavelength whose power is exactly the optimal difference less was unclear to me. I think the idea was that the plant also wants to minimize the wavelength difference, and a given power delta can be achieved with less difference in wavelength in the steeper sloping sections of spectrum power graph.

uj8efdkjfdshf 6y ago

I think the point is that since the power available at these wavelengths vary sharply with frequency in these regions of the solar spectrum, the plant can easily compensate for brightness fluctuations in these portions of the spectrum with minor tweaks to the target wavelength of the relevant photosystems

londons_explore 6y ago
I'd this is the case, it's a shame the article didn't mention it. It makes sense the changing environmental conditions for a molecule could affect the wavelengths of light it absorbs (for example, pH, temperature, etc), but I'm not sure this has been demonstrated for plant pigments?
Sniffnoy 6y ago
I'm confused though -- how can the plant possibly vary this?
- danbruc 6y ago
  In principle plants have several different variants of the light absorbing molecules with different absorption spectra but I don't know how this would actually be regulated. But it is certainly imaginable that plants vary the relative abundance of the different light absorbing molecules or their efficiencies and this could be more or less automatic because of varying conditions like pH or whatnot that affects efficiency or lifetime of the molecules with a simple feedback mechanism or it could be actively regulated by a more complex feedback loop.

floatrock 6y ago

> It might be highly efficient to specialize in collecting just the peak energy in green light, but that would be detrimental for plants because, when the sunlight flickered, the noise from the input signal would fluctuate too wildly for the complex to regulate the energy flow. > Instead, for a safe, steady energy output, the pigments of the photosystem had to be very finely tuned in a certain way. The pigments needed to absorb light at similar wavelengths to reduce the internal noise. But they also needed to absorb light at different rates to buffer against the external noise caused by swings in light intensity. The best light for the pigments to absorb, then, was in the steepest parts of the intensity curve for the solar spectrum — the red and blue parts of the spectrum. I admit there's a bit of a jump there (gotta read the actual article, not the journalist retelling I suppose), but I assume the gist of the math is something like this: Lets say direct green light delivers a maximum 100 "units of photo-energy" -- gonna play loose with the physics to demonstrate the math. When a cloud passes over it, lets say the intensity drops to only 75%. Lets also say for now we always convert the energy at 100% efficiency. So with green light, your 100 units of energy drops by 25 units with each passing cloud. Now lets say blue light delivers only 80 units of energy. When that same cloud passes over, 80 * 75% = 60 units of energy, or a drop of 20 units. So, if your process is sensitive to changes in absolute energy, you would rather have a swing of 20 units for every passing cloud than a swing of 25 units. Yeah, you might get less absolute energy (60 units rather than 75), but if the cost of energy swings in your process was very high, the tradeoff might be worth it. You could also play with the efficiency-of-conversion (ie have higher conversion efficiency at the lower-swing points) for some fun second-order effects. This is just a toy example of what the underlying dynamics could be. Gotta read the actual paper to understand the actual model they developed. https://arxiv.org/pdf/1912.12281.pdf https://arxiv.org/pdf/1912.12281.pdf

wcoenen 6y ago
> Now lets say blue light delivers only 80 units of energy. When that same cloud passes over, 80 * 75% = 60 units of energy, or a drop of 20 units. So, if your process is sensitive to changes in absolute energy, you would rather have a swing of 20 units for every passing cloud than a swing of 25 units. That's not exactly it. The idea is that the blue light absorption can be tuned (presumably by shifting the absorbed wavelengths by a few nanometer) to compensate for external changes. So if the overall light intensity drops 1%, the system responds by shifting the absorbed spectrum to get 1% more power. This only works in parts of the solar spectrum where power varies sufficiently versus wavelength, hence the preference for blue and red.

FriedPickles 6y ago

They do. The paper's point is that plants want to choose two wavelengths with different amounts of average power. This gives the plant a window to tune within to get the desired amount of output power. If the total illumination drops, the plant compensates by tuning more towards the high power wavelength, and vice versa. But the paper makes the point that the tuning mechanism isn't perfect due to internal noise. If the power level difference between the two input wavelengths is too great, then the random fluctuation of the tuning mechanism will itself create a lot of noise in the output. So basically there's an optimal value for the difference of average power between the two wavelengths. Now, why the plant doesn't absorb the peak green wavelength and the closest wavelength whose power is exactly the optimal difference less was unclear to me. I think the idea was that the plant also wants to minimize the wavelength difference, and a given power delta can be achieved with less difference in wavelength in the steeper sloping sections of spectrum power graph.