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Me and a few people are working on a super hot earth where the equator features a humid rainforest climate that sits around 40C - 45C degrees consistently, without any extreme changes in temperature. From what I've been able to gather, there has been no proper analogue for this type of environment in prehistory, since humid climates during the Cretaceous, Permian/Triassic boundary, and the PETM were stabilized around 30 - 35C. 40 degrees is the typical limit for most plants, as the heat makes it difficult for the enzymes required to photosynthesize to function properly. However, there are plants (such as the Arizona Honeysweet) that can photosynthesize in 50-degree heat.

We found that plants that engage in C4 photosynthesis and CAM were at an advantage when it comes to tolerating super hot conditions, so we speculated that grasses, sedges, and other various angiosperm families would dominate these ecosystems. The Moradi Formation in the late Permian appears to have a hot desert ecosystem with annual temperatures somewhere between 30 and 35 degrees, but given the temperature extremes typical of deserts, temperatures likely swung well above 40 degrees on average in the summer. It seems that even with the extreme temperatures, a 25 meter log (likely from a Volztian conifer) has been recovered from the formation, indicating that large trees could tolerate such hot temperatures and that conifers could adapt to the hothouse conditions.

What specific types of plants would do well in the hyperthermal equator? Could Palms and Bamboo adapt well to these conditions?

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    $\begingroup$ Is your world and, subsequently, its life independent of our Earth or is evolution there based on life forms here? $\endgroup$ Apr 22 at 16:27
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    $\begingroup$ For Terran biology you're reaching the limit of photosynthesis. Not that you can't come up with a way around it, or that our plants couldn't evolve higher tolerances as the climate gets hotter scientificamerican.com/article/…. $\endgroup$
    – N Brouwer
    Apr 22 at 16:59
  • $\begingroup$ The fictional planet is not Earth. The autotrophic organisms of the fictional planet are not related to Earth's plants. There are no palms, there are no bamboos. It is extremely unlikely (as in astronomically unlikely) for there to be organisms which use the exact C4 or CAM photosynthetic paths. (And I don't know about whatever country you live in, but I can assure you that plants which live in Romania, both herbs and trees, have to tolerate temperatures above 40 °C. Temperatures above 40 °C occur in summer each year every year in very many parts of our real world.) $\endgroup$
    – AlexP
    Apr 22 at 18:25
  • $\begingroup$ @AlexP ikr, I hate it when people put humans in their worlds, like c'mon, don't they know how unlikely it is for an exact replica of our species to evolve? I wish they were as smart as me $\endgroup$
    – M S
    Apr 22 at 18:52
  • $\begingroup$ This is earth, just wanted to bring that up. This takes place in a hypothetical scenario where Earth has much higher CO2. $\endgroup$ Apr 22 at 20:11

3 Answers 3

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Plantae or "Plants"?

When talking world building people will use the term plants to either refer to members of the Earth based kingdom Plantae that were transplanted to another world or some organism that evolved on another planet that generally fills the same niche and is convergently similar to plants.

If we are talking about modern Earth based plants on an alien world, then sustained temperatures of 40-45°C is just out of the habitable range. Even if some desert plants can survive short periods of temperatures this high, they can't survive sustained temperatures this high because some of thier proteins stop functioning in this range.

You will also note that all the plants on Earth that can survive the greatest temperatures are desert plants. Staying cool can actually be harder in a rainforest than a desert because the air in a rainforest is already going to be saturated or near saturated preventing your plant from being able to perspire to cool down. Also, temperatures are much more stable meaning that there is not a cool night to help cool down the soil and that a heat wave that plants can creatively endure for a little while will last longer, eventually killing the plant.

That said, most proteins can function above 45°C and there are some that can function in temperatures in excess of 90°C; so, if these "Plants" evolved on a world where 45°C is common, then they would not have evolved to be reliant on these more delicate proteins; so, a native plant that can survive over 45°C without difficulty is very much feasible, but they would be as genetically different from plants as Archaea is from Bacteria.

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  • $\begingroup$ Taxonomy tip: "Plantae" is not supposed to be in cursive. Cursive is only used for the ranks of genus and species (specifically to easily distinguish them from higher ranks). $\endgroup$
    – Olle
    Apr 24 at 9:37
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    $\begingroup$ @Olle Did not know that, thanks. Updated accordingly. $\endgroup$
    – Nosajimiki
    Apr 24 at 13:18
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Ever since there was a science tag, that is absent, there has been a nice starting sentence to all answers.

It depends .. on how it deepends.

If its not wet-bulby, your plants can in theory sweat and shut down during the hottest parts of the day. There are loads of plants that "fold" up shop or retract easily damaged parts. Add a slightly reflective layer, sending most of the light back into the sky and you are good.

If it gets wet bulby, we have a problem. Cell denaturation starts at 47°. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC396327/pdf/plntphys00217-0029.pdf Which means damages, that need time to repair- if they can be repaired at all. Your plants will cower in the shade of stones, dead predecessors and grow at night to expand the shade they make for themselves.

Another strategy to protect form peak heat, might be oil(https://en.wikipedia.org/wiki/Castor_oil) film excretion and then subsequent water/gas excretion, to create a heat absorbent foam that insulates. The goal is always to survive the heat.

Another strategy might be to induce a micro-climate change at the hottest hour, creating the famous "midday" rains of the rainforrests. https://www.researchgate.net/publication/46288442_Rainforest_Aerosols_as_Biogenic_Nuclei_of_Clouds_and_Precipitation_in_the_Amazon

So wherever your plants are, there might be morning fog and midday rain, shading them from the worst.

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Most plants on Earth are not adapted to existing at temperatures above 40 degrees C for prolonged periods. Probably because there was no need for them to do so, as most places that do get very hot have other more serious problems such as lack of water. So the proteins of most plants tend to become increasingly degraded above 40 degrees C.

But theoretically the scope available within chemistry is so vast that with sufficient evolutionary pressure it should be possible, given sufficient time to evolve highly heat tolerant proteins.

And in fact there are some on Earth. There are a few places that are extremely hot and extremely wet such as hot springs and cyanobacteria live under such conditions and also photosynthesize at up to 62 degrees C.

Whilst these bacteria are not plants they do demonstrate that very heat resistant proteins are possible. Given a different environment there seems every reason to believe that plants (or some other form of life filling the same niche) might also make use of them.

https://www.nps.gov/hosp/learn/thermophiles.htm

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