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Some folks I write about live in a series of mutually-supporting, mostly self-sustaining agricultural stations/colonies on the edge of a desert, and are attempting to turn said desert greener.

Unfortunately, while they have everything from iceplant to genetically-engineered grass with interconnecting root systems on hand to keep the sand from lifting off and blowing away, they still need something edible to plant in order to increase their self-sufficiency in the long run.

More unfortunately, climate change is involved with this world, and it's gone rampant. The temperature where they live is ~45°C/~113°F - during the coldest parts of winter. It doesn't get colder for them; their version of "winter" is due to their planet being on an elliptic orbit, rather than due to axial tilt, which it basically has none of. Growing season is 1/4 of the Earth-year-length year, and that's pushing it: they plant their crops as soon as the temperature gets below roughly ~50°C/~122°F (long story, religious reasons based off of one of the last working terraforming robots) and hope it isn't too late.

As such, this colony needs some kind of edible plants - preferably as many separate species of them as possible, in order to provide backups in case one goes extinct, to preserve genetic diversity (i.e. one random disease can't wipe out the entire crop), and to keep people sane by providing them with multiple food sources. Additionally, said plants must be as resistant to high temperatures as possible; while I recognize that surviving 122 degrees Fahrenheit is a tall order, anything that can get even remotely close to that is good in my books.

Precipitation and soil are not a concern; the substrate produced by the already-planted soil remediation plants is sufficient for pretty much anything to grow in, and they have a vast network of moisture farms that can provide them with as much water as is necessary. Moreover, it's fine if said edible plants require processing before being eaten, since, on top of that, they possess a high degree of automation; this also means that, say, selectively-bred giant pumpkins that weigh more than a metric ton each are an option here.

However, they have to grow as well as possible in such crazy conditions - not strugglingly, not dying before they produce any edible matter, but well enough to actually be usable as a food source. Moreover, hydroponics aren't really an option at the scales they're working at, and they're trying to build an ecosystem, not a farm. Perhaps initial crop specimens can be selectively bred, but eventually they're going to need to start planting outside the greenhouse, so to speak.

If this is just plain impossible, answer with that - hence the "reality-check" tag.

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    $\begingroup$ Err... green houses? Environmental engineering is NOT the same thing as agriculture. Your colonists are attempting to 'green' a desert? OK fine that's a series of long term, complex, scientific problems. But assuming they know what they're doing and have the technical and logistical resources necessary to complete the task it's doable. Growing food? That's dead easy. (We've been doing it for thousands or years). If your colonists are capable of building structures to live in they can build structures to grow food in. Modern industrial scale agriculture in green houses is actually a 'thing'. $\endgroup$
    – Mon
    Commented Jun 18, 2022 at 12:28
  • $\begingroup$ The key to the problem on your world is the abundant availability of water coupled with the hot dry desert (see my answer below). Plants will not survive in the open at 45 degrees C, but evaporation and shade could create an environment where they could as evaporating water can absorb and carry away vast amounts of heat energy $\endgroup$
    – Slarty
    Commented Oct 6, 2022 at 10:28

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No, you can't grow plants in such a climate.

It is hard for plants to grow at those temperatures. The toughest plant we know of on earth is the: Welwitschia. The plant grows in the desert of Nambia, Angola and sometimes is seen in South Africa. It won't survive your winter and definitely not your summer (seen your winter is 45C at its lowest.) You have to keep in mind that no plant would technically survive those temperatures, in the Kaokoveld desert (where the Welwitschia grows) it normally doesn't get hotter than 30C or around 85F. Very extreme measures would have to be taken to grow this plant.

Welwitschia as food: Some parts of the Welwitschia (not all of them) are edible. Indigenous people eat the cone of this plant by eating it raw or baking it in hot ashes. One of its names, onyanga translates to 'onion of the desert'.

Welwitschia's Genetics: In July 2021, the genome of Welwitchia was 98% sequenced, totalling 6.8 Gb on 21 chromosomes. There is evidence of a whole-genome duplication followed by extensive reshuffling, probably caused by extreme stress due to a time of increased aridity and prolonged drought some 86 million years ago. As a result of this duplication, the genome contains more “junk” self-replicating DNA sequences; this increase in retrotransposon activity was counteracted with a silencing DNA methylation process allowing to lower the metabolic cost of such a large genetic material and improve resilience.

Conclusion: The Welwitschias is one of the toughest plants on earth, though it probably won't survive your climate.

Fun facts:

  • The Welwitschia is displayed at the bottom of the Coat of Arms of Nambia.

  • The South African name for this plant is: "tweeblaarkanniedood" Which roughly translates to: "two leaves can't die."

I hope this helped you? :)

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    $\begingroup$ There are many plants in the Mojave and Sonoran deserts that regularly survive 45C temperatures. Welwitschia may be tough, but it grows in a moderate environment; every city I've lived in the US has had higher highs and lower lows than Windhoek. $\endgroup$
    – prosfilaes
    Commented Aug 17, 2022 at 19:01
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Alien Plants

enter image description here

The other answers say Earth plants cannot grow in places that hot. Fortunately your planet is not Earth:

. . , their version of "winter" is due to their planet being on an elliptic orbit, rather than due to axial tilt,

See that bolded bit? That's how I know your planet is not Earth.

So don't worry about how Earth plants cannot survive here. Just invent some alien plants that can survive here.

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  • $\begingroup$ This was my first thought too, but even if you found alien life that is not toxic to eat, there is little reason to assume it would just so happen to produce all the nutrients that our digestive systems have co-evolved to need. Even if these plants have biochemicals that serve the same roles as ours, if they are not exactly the same (like if the alien plants use sucralose instead of glucose or fructose), your body will lack the mechanisms needed to metabolize them properly, or maybe they just don't have certain essential nutrients like omega-3 or vitamin-C. $\endgroup$
    – Nosajimiki
    Commented Oct 8, 2022 at 14:06
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Build-a-Rainforest

You sound like you are trying to build your own rainforest, but hotter, and with a lot of edible plants. Something that currently isn't possible as a rainforest needs a specific, self-sustaining climate.

It might be possible to slowly expand existing rainforest. Another possibility would be if you artificially create the climate by creating a lot of clouds to locally reduce the temperature and raise humidity. The correct types of clouds (low-hanging 'fluffy' clouds) would reduce the temperature globally and locally. Do this in a wide enough area, above the desert, and you can reduce the temperature quite a bit. A 10-15°C temperature decrease would seem in reach.

The biggest problem would be setting things up, after which the second biggest problem would be making it independent from people. When people stop creating clouds, the rainforest needs to create its own rain clouds (which it actually does) in sufficient amounts to keep the temperature significantly lowered. Because higher temperatures reduce cloud coverage and thus increase temperatures...

As for genetic engineering options, maybe alter normal rainforest plants to produce human-edible crop-bearing fruits.

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45 degrees C would cause terrible problems for food production in the open. But since there is ample water available, local microclimates could be created at a much lower temperature. This could be achieved by using plenty of shade from walls, buildings and natural features. And could be enhanced by using partially sunken gardens, with net shading and especially by the use of large amounts of open water in the shady areas which would provide evaporative cooling.

tunnels could also be dug and chimneys erected to encourage convection currents.

https://www.californialifehd.com/take-a-look-inside-forestiere-underground-gardens-one-of-fresnos-best-kept-secrets/

https://en.wikipedia.org/wiki/Oasis_effect#

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The easiest way to get cooler temperatures is to go underground in caves or tunnels. For example, there is a natural underground oasis underneath the Atacama Desert in Chile, which is the world's driest desert.

You could do this with root plants, with fungi, or with a limited amount of light from the surface channelled to them. You could do a fiber optic skylight for example.

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Use a shade cloth

enter image description here

Shade cloth is often used to protect garden plants that are intended for cooler climates than where you are growing them. By placing plants under a fine mesh, they can still get the sunlight they need without getting burned and drying out. The hotter the day, the bigger difference between being under a sun shade and a direct sunlight. So, for example one test using a 40% shade cloth showed it can reduce surface temperatures from 48.3°C to 35.3°C (27%). Since your planting season averages 45-50°C, we know that you can use them to achieve ground temperatures of about 34-36°C.

Some sources claim the air-temperature under shade is the same as direct sunlight, but that it just feels cooler. And while this can be true, it is not absolutely true. When your shaded area is moist, like a garden bed or a rice patty, evaporation physically cools the space because of the hot air, but the shade cloth prevents the air from re-heating so much like it does in the surrounding area. So, the hotter your climate, the more pronounced the effects of a shade cloth are.

This would allow you to create a suitable growing environment for many Earth based "hot weather" crops including rice, corn, okra, eggplant, tomatillos, squash, melons, and hot peppers.

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