# Creating plants that do not rely on photosynthesis but still create oxygen

My planet has an increased axial tilt, resulting in crazier winters and summers and higher temperatures. For most places, the temperature never drops below freezing - even in the winter, but the days can be as short as four hours during this time. I want my fauna to reflect this, and rely less on photosynthesis (which will also give me the chance to make everything less green!). However, I also want quite a bit of oxygen in the atmosphere (around 30 percent of it to be this way). I've already looked up fungi and dodder style plants, but they don't appear to create oxygen.

My question is, how could I go about creating plants like this in a scientifically plausible manner?

• 30% oxygen would cause insects and dinosaurs to grow Very, Very Large. Also, lots of brush & forest fires. May 23, 2017 at 0:46
• You're right! I also pre-built that into the world. Fire could possibly even start on wet vegetation, so first I came up with an idea where fungal-ish trees grow scots pine like bark, which bursts open and spews heavy, non-flammable powder to snuff the flame, or maybe inert gases, although I like the powder idea. Also, the sentient life forms on the planet evolved to be able to dig quite quickly, allowing them to fight the fires with fire lines with relative ease. May 23, 2017 at 0:50
• I also thought about having uniquely large amounts of beryllium in certain types of vegetation to help them endure better. May 23, 2017 at 0:53

Plants create oxygen as a byproduct of photosynthesis, using energy from sunlight to break apart molecules of water and carbon dioxide and reform them into carbohydrates (such as glucose) and oxygen. If you want a substantial amount of oxygen in your atmosphere, that oxygen has to come from somewhere- either from oxides in the ground (most likely quartz crystals or metal ores), or from CO2 in the air. And liberating oxygen from any such source requires energy. That energy has to come from somewhere.

There are a few exothermic reactions that release oxygen (such as the "oxygen candles" popular on submarines: $3NaClO_3 + 2Fe \to 3NaCl + Fe_2O_3 + 3O_2$), but their reactants (sodium chlorate and iron metal, in this case) have to be more reactive than oxygen in order for the reaction to work at all. By the time life starts developing on your planet, any such compounds will have already broken down, and any oxygen released will be bound up in things like quartz, iron oxide, and carbon dioxide.

You mention fungi and the parasitic dodder plant, and that they do not produce oxygen. This is true. Fungi are actually more closely related to animals than to plants; they produce energy by breaking down biomass produced by other organisms and reacting it with oxygen to produce water and carbon dioxide.

In order to produce oxygen, your "plants" will need to need another source of energy to break down oxygen-containing compounds (most likely carbon dioxide) in order to get at the non-oxygen components, and release the oxygen as a byproduct. All Earth plants power this process with sunlight, because it's abundant and it works. However, some organisms have other energy sources. The chemosynthetic bacteria in giant tube worm guts, for instance, create carbohydrates by reacting carbon dioxide with hydrogen sulfide:

$$12H_2S + 6CO_2 \to C_6H_{12}O_6 + 6H_2O + 12S$$

This produces solid sulfur as a byproduct, rather than oxygen; however, a chemosynthetic organism with a source of hydrogen could react it with carbon dioxide instead:

$$6H_2 + 6CO_2 \to C_6H_{12}O_6 + 3O_2$$

Such a hydrogen-eating organism might release oxygen as a byproduct; or, more likely, it could react the oxygen with more hydrogen to produce water and quite a bit more energy.

$$12H_2 + 6CO_2 \to C_6H_{12}O_6 + 6H_2O$$

However, I doubt that chemosynthesis will play a major part in your planet's ecosystem. As on Earth, chemosynthetic organisms will be relegated to dark, oxygen-poor areas with sources of reactive chemicals such as hydrothermal vents at the bottom of the oceans. Instead, the foundation of the ecosystem will be based on photosynthesis.

You've got a planet with a high axial tilt where, even in the dead of winter in the polar regions that get only a few hours of sunlight per day, the temperatures rarely drop below freezing. There's only two ways for that to be possible: either there's some serious greenhouse effects going on, or the lower latitudes and the summer months get a ridiculous amount of sunlight. If there's a strong greenhouse effect, that means that there's a lot of carbon dioxide, methane, or other greenhouse gases in the atmosphere. Gases such as methane will quickly react with all the oxygen that you have; while the presence of large amounts of CO2 indicates (to me, at least) that your plants aren't doing a very good job of absorbing it and converting it into oxygen.

Which leaves sunlight. And lots of it. Photosynthetic plant life will be even more abundant on your planet than it is on Earth.

However, you also note that you don't want everything to be green. No problem: there are many different pigments that Earth plants use for photosynthesis, with green chlorophyll only being the most common. See the table here: chlorophyll a is the familiar green stuff, chlorophyll b is yellow, chlorophyll c is blueish-green, chlorophyll d is found in red algae, and chlorophyll f absorbs far infrared light, so it probably appears colorless to our eyes.

No one's quite sure why chlorophyll a, which mostly reflects green light, is the most common chlorophyll on modern Earth. After all, the Sun produces more green light than any other color, so it seems like the most common types of plants would be adept at absorbing green light.

Perhaps the first photosynthetic bacteria to evolve on Earth were good at absorbing green light, and blanketed the surface of the oceans. Other bacteria evolved chlorophyll a to take advantage of the red and blue light the surface microbes left behind; and then the purple surface bacteria all died out... for some reason. Maybe. Or maybe chlorophyll a just popped out of a random mutation, worked well enough, and evolution ran with it. There's no way to know.

If you want polychromatic flora, just go for it. There's no reason why plants that evolve on another planet need to look just like the ones here.

• @Someone_Else_37 Wow.... that actually fixed 90% + of the problems I was having... all the research I had done never once pointed me toward the understanding that there were different types of chlorophyll... And yeah, I didn't even think about the heat in that sense, I just wanted a more tropically inclined planet. That chart will definitely help! Thank you!! May 23, 2017 at 2:22
• One interesting theory about the optimal color for photosynthetic organisms is that they tend to absorb the most steady light in their environment, rather than the most intense. Green wavelengths, while powerful, tend to fluctuate wildly depending on how direct the sunlight is at a given moment, and absorbing too much energy without preparation can cause cellular damage. The scattered blues and weaker reds provide a weaker, but more consistent, energy input. quantamagazine.org/… Feb 9 at 8:41

You need a source of energy for the life-form to live. Other than sunlight, we have chemical energy in real life.

It produces oxygen as a waste product when it harvests carbon from the air as a source of material, so you can decouple that from photosynthesis. Look up autotroph.

No reason why this life-form would be green, though.

Poke around in existing questions here on WB! I recall discussing “flex fuel” life-forms that could readily shift between available energy sources, which is what you want here: use photosynthesis when possible, but use chemosynthesis in various forms if that’s the only energy available.

※ Here's one place I touched on it. But I think the idea of adapting organelles has been written up in more detail, too.

• Thanks! And perhaps I should clarify on the green bit. Chloroplasts that are used in photosynthesis have a green pigment, which is why so many plants are so green. So, in my mind, if i used photosynthesis, making the plants any other color than green would put them at a disadvantage on a planet with odd seasons. May 23, 2017 at 0:26
• Look for the other posts — imagine a variety of organells besides chloroplasts, as more autonomous endosymbiotes. Shifting the population and acquiring different ones allows the complex cells to adapt to different energy sources. May 23, 2017 at 0:31
• I don't think that chemosynthesis creates oxygen. May 23, 2017 at 0:40
• @Xenobear not to worry; the use of oxygen is true for that specific ecosystem, and is not needed for every possible chemical reaction that gives energy release! I do think that the life in rocks 3 mikes deep does not use free oxygen — I’ve seen descriptions that it “breathes” iron. And here May 23, 2017 at 5:32
• Also see this article for a story of life surviving when it was cut off from light for 1.5 million years. Now that you know about these things, you can search and find much more info online. May 23, 2017 at 5:36

You can make a chemosynthesic plant.

Imagine something like bacteria, it makes atp but not nadh from an respiratory electron transfer chain that is powered by something like reacting rocks to sulfuric acid(sulphate reducing process), and, now because the synthetic machinery may have been made in a photosynthetic organism, the bacteria can not reduce carbon dioxide without making oxygen in the process(reverse electron transfer chain) and the bacteria have no machinery to consume oxygen.

Now you get an organism that uses a fuel cell powered by suboptimal reactions(sulfur oxidization by iron, oxidization of h2s by manganese, metallorespiration, oxidization of iron by nitrates or sulfates, etc.) to drive a high level energy consuming reaction(like the photosynthetic electron transfer chain) that makes the actual material that organism uses, the process that gives out oxygen.

Aerobic metabolism takes long time to evolve(if impossible to develop by evolution alone), and if that happened in somewhere outside of bacteria...... expect to see a lot of deep oxygen sources and oxygen generator that does not depend on the sun.

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Recently scientists have discovered two separate species of microbes that use two independently different novel metabolic pathways to produce oxygen without photosynthesis. So it might be possible for non-photosynthetic plant on your planet to produce oxygen without photosynthesis using one or a combination of these two pathways. Here’s two articles on these microbes, if you’re interested in having a read for inspiration: https://www.sciencedaily.com/releases/2022/01/220106143640.htm

https://www.mpg.de/bacteria-produce-oxygen-even-without-light