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I am currently building a planet that weighs about 4 earth masses and it's radius is 2.3 times larger than that of earth's. It is an ammonia planet (as the title suggests), and has ammonia oceans with some dissolved water ice, methanol, hydrazine, chlorethane, and salts (sodium, chlorides, sulfates, potassium etc.). The average temperature is about 225ºK on the planet and the avg pressure at sea level is about 4 atm.

I've made quite a few different questions about floating plants so far, and this question and this other question help summarize the structure of this class of floating plants, but if you don't want to click on the links, here is a brief summary.

These plants float to avoid predators and get more light to power an anaerobic version of photosynthesis (that means exotic biochemistry). They are relatively small and have gas bladders with methane in them to float, and can open their stomata to let in regular air and sink. Some have tethers that let them hover, but these are generally present at lower altitudes, and we will be dealing with floating plants present at higher ones.

Most of these plants use eumelanin (creating black leaves) or the simple pigment retinal (creating purple leaves), but I'd like some plants to evolve a variant of chlorophyll. In my planet, which is filled with ammonia, ozone can't form, so all life is resistant to UV and harder types of radiation coming out from the star and there's an awful amount of useless radiation coming out from the star... However, one floating plant (and all floating plants are exposed to more radiation as they go higher up) decides to start using chlorophyll to absorb light, specifically chlorophyll with beryllium instead of magnesium in its core in addition to its use of retinal at first.

Beryllium has a higher binding energy than magnesium according to the first answer of this question, so it can absorb higher frequency wavelengths of photons. My question is that is this use of beryllium here useful enough to justify the costs of using another pigment altogether? Remember that these plants aren't altogether using this version of chlorophyll. Instead, they are using them to increase the amount of light they can absorb and power their version of photosynthesis.

Bonus points if you can tell me what color the alternative chlorophyll will make the leaves!

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  • $\begingroup$ Remember that here on Earth chlorophyll can only really use red and deep red light. The ability of photosynthetic life to use the rest of the visible light spectrum depends on the accessory pigments (also known as antenna pigments) which absorb light of various wavelengths and fluoresce the deep red light which can be used by clorophyll. $\endgroup$
    – AlexP
    Commented Apr 13 at 21:59
  • $\begingroup$ @Neil Iyer maybe your plants need to use higher frequency light primarily due to their resistance against lower frequency light. Like their resistance makes absorbing lower frequency light hard so they opt for the higher frequency ones. Your leaves may red to orange/yellowish as they are lower frequency light which is likely going to be reflected. $\endgroup$ Commented Apr 14 at 10:36

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Note: This is probably a bit of a wonky answer so if i got anything wrong please correct. So i can edit this answer correctly.

Absorbing higher frequency light:

  • More Energy: Light of higher frequency has more energy than low frequency light. So specializing in absorbing it may be more advantages. This way your plant can get more energy out of their photosynthesis.

  • Reflective Texture: I admit that on this one i am very uncertain. So feel free to correct me on this. So what if the resistance your plants developed to UV-Radiation had the unfortunate side effect off making it more difficult to absorb lower frequency light. This would necessitate the plants opting for higher frequencies to get their energy from.

Leaf color:

  • A leaves color is determined by what light frequency it reflects. On earth this green light thus leaves are green. Though on your world if your plants reflect lower frequency light they would be probably red to orange/Yellow on color. Though they may also be purple if they reflect more higher frequency light like purple light.
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    $\begingroup$ Now that I think about it, these plants of they only use beryllium chlorophyll will be white to humans because they reflect all visible light and use UV instead. However, if they also use another pigment like retinal or eumelanin, they might just look light purple or gray instead. $\endgroup$
    – Neil Iyer
    Commented Apr 14 at 23:09

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