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I'm worldbuilding a whimsical, leisurely world where the livin is easy. I was thinking about, "What would put agriculture/industry on Easy Mode?"

One answer that suggests itself is increasing photosynthetic efficiency: plants are the basis of most goods (food, fuel, fiber, even meat), and if they could capture more incoming energy, people would have more of everything.

Doing some research on this question led me to C3, C4, and CAM plants. There is already work done to make C3 plants C4. Is this the route to go down for my worldbuilding? Should I make all plants in the world C4 producers? Or is that impossible or detrimental for some reason I've overlooked?

Another possibility: I found this research about adding enzymes that break down glyoxylate into CO₂ which is then reüsed instead of going to waste. "The end result is 24% more biomass."

Should I go with the glyoxylate-breakdown route? The C4-for-all route? Both? Other?

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  • $\begingroup$ If you want to build a world that does X, make it do X. Don't spend forever and a day trying to justify why X can exist, because that's chronically unimportant. $\endgroup$
    – Ian Kemp
    May 26 at 16:18

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There is an easy method of increasing plant production: more CO2. A quote from that article:

In those experiments artificially doubling CO2 from pre-industrial levels increased trees’ productivity by around 23 percent...

This article includes tests on the net effect on crops in greenhouses, showing that the optimal level for most plants is in the range 1000 to 1300 ppm, compared to the typical outdoor values of round-about 340 ppm. That is, three to four times the ordinary values.

Many species of plants originated during periods with much higher CO2. Now that CO2 levels are rising due to industrialization, the entire planet is greening. One can almost imagine the forests saying "Oh! It's a delightful breath of stale fetid air! Mmmmmm!"

By the way, humans are OK with that sort of level. It may require some adaptation and acclimation. But they are not dangerous to health. Humans start to have effects round about 5000 ppm.

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    $\begingroup$ This is a good idea. I've actually used it in greenhouses before. $\endgroup$
    – wokopa
    May 25 at 15:07
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    $\begingroup$ I think humans are demonstrably affected (in a 'negative' way) by higher CO2 concentration starting from only 800 ppm. The problems are of the cognitive kind. (Hence the recommendation to regularly vent classrooms etc.) $\endgroup$
    – Vergilius
    May 26 at 9:18
  • $\begingroup$ The study about the greening earth sounds a fake. 1) The image shows as green urban area. 2) Arable land which makes up the vast majority of the Earth surface is green only for some periods of time. 3) Logged land. Turning forest to brush reduces greening, but is not visible. 4) Roads, rail and other transport infrastructure, like urban areas, in that image are not visible. Are they counted as green as well? $\endgroup$
    – FluidCode
    May 26 at 19:32
  • $\begingroup$ Still about the fake study. The concentration of CO2 as a percentage is increasing because the relative initial value was small. But in absolute terms it did not increase so much that it could so dramatically affect plant growth. $\endgroup$
    – FluidCode
    May 26 at 19:37
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    $\begingroup$ @FluidCode Just realized that Boba Fit already linked to the NASA article... You made a comment without clicking on the link and realizing "Oh, this article was written by NASA, one of the most reputable scientific organizations in the world... Its probably true." And instead jumped to "It is fake... Good job... $\endgroup$
    – Questor
    May 26 at 21:25
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The metric of "efficiency" doesn't exist in a vacuum. CAM photosynthesis works well in hot, arid conditions when plants using other systems risk being dried out. Even in the C3 to C4 link you gave above, you can see notes like "C2 photosynthesis... has the advantage of requiring fewer steps of genetic engineering and performing better than C3 under all temperatures and light levels." which under some circumstances can make it a better choice than C4, especially for higher latitudes. You don't say anything about the climate in which your plants are growing, but it makes a big difference here!

Plausibly, your future genetic engineers might be using all the techniques they can usefully combine in order to maximize yields under some particular set of conditions. We don't know what that combination of modifications could be, because we haven't tried them yet. A reasonable assumption is probably to pick one or other of the things you linked that are actually being experimented with in the real world.

The safest solution is to not mention the technical details at all, because there's scope for getting stuff unambiguously wrong in making such claims and there's no real benefit to your story or setting.

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No, it couldn't.

Just capturing more carbon is not enough. For more biomass, the plants would require correspondingly more of other nutrients as well, which would become a new limiting factor because improved photosynthesis does not create more of them.

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    $\begingroup$ Yes it could. "The end result is 24% more biomass" is a quote from a real-world study, linked in the OP. $\endgroup$
    – Starfish Prime
    May 25 at 14:15
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    $\begingroup$ @StarfishPrime, thank you. No, it couldn't; the 24% increase in biomass required germinating the plants in a greenhouse in a pot filled with a soil mix, then transplanting them into prepared plots, spacing the plants just right, and watering 'as needed'. You neglected these inputs though; no wonder efficiency appears higher to you. $\endgroup$
    – ihaveideas
    May 25 at 14:53
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    $\begingroup$ And yet simliar plants grown in the same circumstances without the modification did not have substantial additional biomass, despite the other circumstances. This is because the efficiency of production of biomass in the modified plants is higher given the same nutrient sources. $\endgroup$
    – Starfish Prime
    May 25 at 15:02
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    $\begingroup$ Your answer assumes that growth is already bottlenecked by other nutrients. It's possible for this to be so, but will not always be so. $\endgroup$
    – Christopher James Huff
    May 26 at 1:36
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    $\begingroup$ @Katy, thank you. It's easier to understand by keeping in mind that there is not just one limiting factor. Tropical rainforest needs nutrients and water and high temperature year-round and high insolation; take away any one of these things and its supposed higher efficiency drops to zero because it can no longer grow. Going back to the original conversation, more efficient photosynthesis does not lift any of these limits; it just makes the plants reach them quicker. For a real-life example, consider how weeds grow quickly only to eventually be outcompeted by other plants. $\endgroup$
    – ihaveideas
    May 26 at 9:28

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