4 ms·
> 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 sunli
by 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.
- rini17 6y agoAhh I get it. Maybe the leaves even actually change colour when shaded, but our eyes just aren't sensitive enough?
- Sniffnoy 6y agoI'm confused though -- how can the plant possibly shift this?
- wcoenen 6y agoBiological light harvesting complexes[1] act as an antenna network. I guess the shape and other properties of such a complex change depending on conditions. The paper doesn't really try to explain the biological tuning mechanism. Instead, they created a model of an antenna network capable of tuning. As in, this model had a bunch of parameters describing how it captured light and tuned. Then if they optimized those parameters for stability given the light spectra that different plants are exposed to, they found that their model would reproduce the actual absorption spectra of those plants. This strongly suggest that the plants have done the same optimization by evolution. [1] https://en.wikipedia.org/wiki/Light-harvesting_complexes_of_green_plants https://en.wikipedia.org/wiki/Light-harvesting_complexes_of_...
- CydeWeys 6y agoAnd on what timescales does this timing occur? Are we talking seconds? Or days, i.e. accomplished by growing different structures?
- h2odragon 6y agoFWIW, hardening seedlings to sunlight from a greenhouse is all about switching their spectrum, and it takes 3 to 7 days depending on what plant you're talking about. Gardener's rule of thumb. 4/6/8hr exposure etc. I wonder if anyone has used RGB LEDs and tormented plants with short cycle color changes yet? There's much anecdata and debate over spectrum vs efficiency in indoor gardening, but it's faded as power density became more obviously dominant, i think.