BIOLOGY | PART 8 | PLANT COLOR & SUNLIGHT - PART 1

NOW YOU CAN EAT SUNLIGHT!

history of the entire world, i guess - Bill Wurtz

 

PHOTOSYNTHESIS...

...A word derived from the Greek phos, "light", and sunthesis, "putting together", it is the name of a physical-chemical process, at the cellular level, carried out by chlorophyll living beings, which use carbon dioxide and water, to obtain glucose through the energy of sunlight - which is used to trigger the reaction, according to the following equation:

6 H₂O + 6 CO₂ + energy → C₆H₁₂O₆ + 6 O₂

Photosynthesis initiates most of the food chains on Earth. Without it, animals and many other heterotrophic beings would be unable to survive because the basis of their food will always be on the organic substances provided by green plants - their characteristic green color comes from the pigment chlorophyll.

Chlorophyll is a chlorinic pigment with four pyrrole rings linked by methyls, and a fifth ring absent in other porphyrins, a group of compounds to which it belongs and which includes compounds such as the heme group. At the center of the ring is a magnesium ion (Mg2+) coordinated by four nitrogen atoms. The compound is called Pheophytin when magnesium (or another metal ion) is not in its center.

Although green Chlorophyll (there are 6 types of chlorophyll) it's the most common pigment in Earth's photosynthetic life, it's not the only photosynthetic pigment, and some don't even produce oxygen, processing hydrogen sulfide instead.

Some known plant pigment groups and their colors (reflected wavelengths) include:
Carotene, orange
Xanthophyll, yellow
Phaeophytin a, gray-brown
Phaeophytin b, yellow-brown 

Chlorophyll a, blue-green
Chlorophyll b, yellow-green

Anthocyanins, vary from vivid red, pink, blue, to violet depending on how acid or basic the plant is.

 

Other pigments in microorganisms and some algae include:
Phycoerythrin, bright red

Phycocyanobilin, blue

Phycoerythrocyanin, magenta 

Phycourobilin, bright orange

Phycoerythrobilin, red

Bacteriochlorophylls a&b, purple

Bacteriochlorophylls c/d/e, green

 

DOMINANT COLOR DISCUSSION

The topic of determining a planet's main vegetation color is rather slippy, to start with, most discussions assume that only one type can prevail - even though this logic falls short when we look back at Earth because we have so many alternative pigments, of course, for some reason we are yet to fully understand, green chlorophyll ended up being the most used on Earth - it would be reasonable to look at our Sun and say - well, it's emission spectrum is pretty broad, it's understandable that we would have a broad absorption spectrum for photosynthetic life too - that may not be the case the further from a solar-analogue you get though.

One away to look at these cases is the Peak Spectrum theory, which assumes that plants would evolve to absorb the most abundant wavelengths from it's star, ie, planets around hotter and bluer stars would have reddish vegetation because they absorb blue-ish light, planets around cooler and redder stars would have anywhere from blue plants (both to reflect dangerous bursts of UV) to dark/black plants because they absorb most of the visible spectrum.

The Problem with this way of thinking, is that when you get to yellow stars like our sun, the plant color would have to be purple... Because the plants would absorb green-yellow light from the peak spectrum, and reflect blue and red, making purple to our eyes.

Using complementary colors to the peak, like our plants do, absorbing blue and red, reflecting yellow-green light, renders interesting arrangements.

Here is a simplification of the two models (peak reflection or complementary reflection):

Peak Emission colors and complementary colors to those, organized by star temperature, to the right - some common photosynthetic pigments and their colors

Bellow, a more complete table, and a luminance filter for CMYK coloring, accounts for the monochromatic effect in lighting, ie, even though blue plants could appear in a planet around a red dwarf, the lack of blue light photons would make the leaves actually look black - on the case for bluer stars, colors other than blue would look unsaturated.

An extension of the color table shown before

Having that in mind, and the range of human vision, here is my rendition of what plant-color gradients could look like:

Primary emission colors, variations on pigment concentration and mixtures could yield more saturation on different cases

Complementary colors, naturally range from dark blue to magenta to light yellow, the luminance difference would unsaturate the colors a little bit

While using the table, pick your star color temperature, and choose if you're either reflecting or absorbing the peak emissions, then with that color, pick the pigment that most resembles that color.

For example, for an F9V star, with 6000K temperature, the available colors are around light blue and rusty orange - we could then use a mix of neutral anthocyanin and chlorophyll-a, xanthophyll and petunidin (could be yellow-green, green, and cyan depending on the balance) phaeophytin-b and carotenoids, phaeophytin-a and acid anthocyanin, acid anthocyanin and carotenoids, the list could go on with different shades and proportions.

 

THE CASE FOR PAART

Following the so pre-established parameters, we have that plants on Paart could either have colors centered around pastel red, or turquoise-green.

That will be up for voting by the Project Paart crew, and until we decide - stay tuned, and good gardening!

- M.O. Valent, 22/09/2020