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RandomFactor writes:

Green is the color "that reigns over the plant kingdom", photosynthetic plant surfaces typically reflect about 10% of incident green photons. Logically this seems wasteful of Kingdom Plantae, as Green is where most of the energy of the sun is radiated. So why are plants green? Quanta has the story that tells the tale of the tincture and notes that the answer "might apply throughout the universe."

According to Nathaniel Gabor, a physicist at the University of California, Riverside and his team, who developed a model for light-harvesting systems of plants below a canopy of leaves:

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.

The model's predictions matched the absorption peaks of chlorophyll a and b, which green plants use to harvest red and blue light. It appears that the photosynthesis machinery evolved not for maximum efficiency but rather for an optimally smooth and reliable output.

"sometimes — evolution cares less about making biological systems efficient than about keeping them stable."

Journal Reference:
Trevor B. Arp, Jed Kistner-Morris, Vivek Aji, et al. Quieting a noisy antenna reproduces photosynthetic light-harvesting spectra [$], Science (DOI: 10.1126/science.aba6630)

Original Submission