Effect of low gravity on plant life?

undormant · 2014-08-15 08:20:07

Hi,

I've looked online for this info but all I can find is the effects of zero gravity on plants.

I'm wondering how plants and trees etc would grow on a terraformed Mars?

We assume lower gravity would mean taller and stronger trees? Do we have evidence for this assumption?

I'm a writer so curious to know the likely answers.

Please help.

R

Void · 2014-08-16 09:51:29

I would guess plants would mostly try to follow a genetic programming mandated by 1 gee.

However trees might not be damaged as easily by thinner winds, and lighter snow loads. But trees are going to be hard to grow on Mars for a long time I expect.

RobertDyck · 2014-08-16 16:58:44

Well, Biosphere2 found something no one was expecting. Trees in their giant greenhouse didn't experience wind. Without wind to stress the branches, they didn't grow strong enough to support their own weight. They would grow until too heavy, then break off. This was solved with big fans.

Since tree growth is determined by stress, that would imply that lower gravity would stress trees less, so branches and trunks would be thinner. Not a big difference, but something.

Most plants other than trees grow toward light. Because Mars has the same length of day (less than an hour difference) expect they'll grow the same.

Many plants requires oxygen. Although they produce oxygen, they require a certain concentration. Wheat requires the same amount of oxygen as humans. Although pretty much all plants grow better with more CO2. In fact, most plants have a problem: not enough CO2. The high O2:CO2 ratio causes a one enzyme in the Calvin-Benson cycle of photosynthesis (also known as the dark reaction) to produce a waste product instead of what it should. This is solved by increasing CO2. A few plants do this, they're called "C4" because they produce a chemical that has 4 carbon atoms. That intermediate is broken down to produce more CO2 in plant tissues. Although the process requires some energy, it makes photosynthesis more efficient so in Earth's current atmosphere plants that do this grow faster. Most weeds are C4, but most food crops are not. Of course that means weeds grow faster than crops, frustrating farmers. But corn is a C4 crop, which is why it's so efficient.

Some greenhouses increase CO2 concentration to speed plant growth. But if you increase it to 10% for optimal plant growth, workers need to wear breathing gear. That much CO2 is lethal for us. Terraformed Mars would have much thicker atmosphere than it has today. Nothing but archaea could live there. Warming Mars sufficiently to sublimate dry ice would increase pressure. One scientist estimated 300 millibar pressure. I've asked scientists to update that, but most are afraid of anything that hints of terraforming. At 300 mbar, that's roughly 30% of Earth's pressure. But if all you do is warm the planet, then current atmosphere would be swamped in CO2. Currently it's 95% CO2, but with that much more it would be well over 99%. Trees and wheat wouldn't survive, not enough oxygen.

You could start with cyanobacteria. Cover wet ground with transparent plastic, not tightly sealed but enough to allow O2 under the plastic to build up. The plastic would have to have openings to let rain through. O2 would leak out. But if concentration of O2 and humidity under the plastic is enough, then sphagnum moss could grow. Sphagnum moss + cyanobacteria forms a peat bog. Or a different moss with a different variety of cyanobacteria to form lichen. These could grow fertile soil, and build up enough oxygen to grow trees. Black spruce can grow right in a peat bog. It's acidic soil. Forbes will grow: similar to grass but able to handle soil that acidic. As well as blueberry, raspberry, wild strawberry, saskatoon berry (aka Juneberry), cranberry, huckleberry, sarsaparilla (for root beer), lingonberry (aka cowberry, partridgeberry, mountain cranberry or foxberry), and cloudberry. Trees themselves could lift the plastic sheet, holding in enough O2 for plants. But it would be too much CO2 for humans. And Mars soil today is alkali; sphagnum moss creates acid to leach nutrients from rock, a major way it creates soil from solid rock, but that takes millions of years. Terraforming would have to help it along.

Years ago I proposed building an artificial peat bog by grinding rock to fines, and put a slow-sand filter under the bog every so often. With a pole reaching above soil to support a solar panel with battery to run a pump. Peat requires stagnant water, so ensure the pump does not aerate water. But the water would go through a lime water treatment system to remove calcium and magnesium: water hardness and alkali. And the pump would circulate acidic water from peat moss through the ground-up rock flour, speeding the process of breaking down rock. A couple decades to convert ground rock to clay, loess, and peat: rich soil for agriculture. Once soil is suitable, the lye removed would be added back to neutralize soil pH. Some plots would be planted with trees, as described above, creating Boreal forest. Other plots would have lye added to neutralize soil pH, going directly from moor to farmland.

But yea, trees require substantial atmosphere, and enough wind to stress branches to grow strong. Expect terraformed Mars to have snow in winter. Trees need to grow strong enough to survive snow load. So not enough wind in summer means trees won't survive winter.

And how will plants handle the longer year? One Mars year is 668.5991 sols (Mars days), or 686.971 Earth days. I'm sure some plants will adapt, taking advantage of whatever growing season they have, while others won't. I don't know which ones.

Last edited by RobertDyck (2014-08-16 17:03:51)

Tom Kalbfus · 2014-08-16 23:26:21

There are other ways to produce oxygen, such as splitting water into hydrogen and oxygen, all that requires is direct current electricity. Hydrogen tends to escape very easily into space, especially if its on Mars. Now Venus has 60 bar of oxygen in its atmosphere as part of carbon dioxide, that would make a 2 km deep ocean on Venus. Mars doesn't have nearly as much water, but then doesn't need it to make about 0.2 bar of oxygen either. There is a lot of oxygen locked up in the Martian rocks as well. 0.2 bar of oxygen is all you need to breathe, you probably want some other gases as well, such as 0.1 bar of nitrogen, and 0.01 bar of carbon-dioxide which Mars already has. As you split water on mars, you keep on bombarding it with icy comets and asteroids to replace the water you lose. not a big problem as the asteroids and comets have to fall down hill to get to Mars.

undormant · 2014-08-17 07:48:34

Very interesting stuff, but even a terraformed Mars would still have stronger winds than Earth due to low gravity? Meaning more pressure on branches making them strong enough for winter?

R

RobertDyck · 2014-08-17 09:10:29

Mars is farther from the Sun than Earth, and one sol (Mars solar day) is 24 hours, 39 minutes, and 35.244 seconds. That implies that once Mars has a thick atmosphere, winds will be similar to Earth. Wind is driven by temperature difference. Today the thin atmosphere allows great temperature difference between the surface and upper atmosphere. The surface can get to +24°C while it's 10°C colder just 2 metres above the surface, and -80°C at the altitude of clouds. That drives extremely high speed wind, but that same thin atmosphere means the fast wind doesn't have much force. Once Mars has a thick atmosphere (~0.3 bar) then temperature differences won't be as great. Earth can get great differences as well: stratosphere can be -70°C during the summer. But difference between ground temperature and just a couple metres above the soil is not that great. Actually, extreme difference in temperature from the upper troposphere (lower atmosphere where we live) and surface of ocean is what causes hurricanes.

Mars will have strong winds as long as dry ice polar ice caps exist. But creating enough atmosphere for humans to walk outdoors without a spacesuit? That requires sublimating all that dry ice. In fact, we have to sublimate dry ice in deep soil. That will take some time. CO2 freezes to form dry ice snow at -78.5°C, so warming above that temperature will cause it to begin to sublimate. Dry ice melts at -56.57°C at 1 atmosphere pressure, so this will greatly accelerate sublimation. Warming water ice to melt it would require first sublimating dry ice in that region.

Terraforming is a process that will take a lot of time. Some people explored the idea of bombarding Mars with thermo-nuclear bombs to warm it quickly, but that would create massive radioactive fallout. By the time that radiation decays, Mars would have re-frozen. So that doesn't work. The best idea so far is deliberately create greenhouse gasses. Look at Earth: humans are creating global warming. So deliberately cause global warming on Mars. Build massive chemical factories to spew industrial quantities of greenhouse gasses. You don't want to release chlorofluorocarbons (CFCs) because that destroys ozone. But you can release perfluorocarbons (PFCs) and sulphurhexafluoride (SF6) which cause global warming without harming ozone. I took their calculation of how much, and once calculated what it would take to do that. An ore processor as large as one of the processors at the Alberta tar sands; 4 such ore processors at each site on Mars, with 10 such sites operating continuously 24:7 for 13 Earth years. Once greenhouse gasses are in place, it's a blanket to hold heat in. So it will take more years for heat on Mars to build up. Then more years again for all that dry ice to sublimate. Then more years for water ice to melt. Eventually you have a planet with a CO2 atmosphere with clouds and rain, rivers and streams, lakes and a single salt water ocean in the northern hemisphere. Hellas Basin is a giant asteroid crater, it would fill to form a salt water sea.

It would take a nuclear reactors to power all that. Mars Global Surveyor already identified thorium on Mars. Some work has been done to develop nuclear reactors fueled by thorium instead of uranium; India has done the latest work and build a prototype. Military doesn't like it because thorium can't be used for nuclear bombs, it releases energy slowly over days or months. But that's one reason why it's so good. And there is only one isotope in nature of thorium, so 100% of mined thorium is fuel. While only 0.7% of uranium is U-235, so uranium reactors are actually very inefficient. There's roughly 3 times as much thorium as uranium on Earth, so *LOTS* of thorium. That proportion is probably the same on Mars. Miners consider thorium to be an indicator mineral for uranium, but I'm arguing to use thorium itself.

But this means strong winds while Mars is being transformed. But once terraforming is complete, Mars should have about the same wind as Earth. And that should be enough wind for strong trees.

Last edited by RobertDyck (2014-08-17 13:55:21)

Void · 2014-08-17 09:45:44

I mostly agree with RobertDyck.

But I will roll it out my own way.

I recall that Josh suggested that Mars may have 100-1000 mb of resources that could be vaporized to thicken an atmosphere. I am guessing that that will be mostly CO2.

@1000, it would be approximately as greenhoused as the Earth would be at 500 mb. There is the matter of also using special greenhouse gasses, and that could make it warmer than otherwise if they were maintained.

@100 it would be possible to have a biosphere, but it would be subject to a lot of cold conditions at night and during the winter. A challenge to life.

So, unless some unusual discovery or new method is found it is gong to be on the average significantly colder than Earth even if terraformed.

This suggests high latitude Earth trees if any trees, or alpine trees.

So tropical is unlikely without the unusual use of super greenhouse gasses.

Tropical or sub tropical would be nice, but then you have the problem of the dominance of CO2, and lack of Oxygen. In time, I suppose, and eventually a conversion could happen, but that will be a lot of time.

I will go back to a different vision.

I would say the options are dominantly non-fluvial, and fluvial conditions.

Mars is non-fluvial now and cannot even keep it's CO2 atmosphere fully inflated. So getting that fully inflated would be an early objective. An identified CO2 content in the Southern polar ice cap would be sufficient to inflate the atmosphere to 11 mb. That level would allow for snowfalls, and temporary melt streams in places.

That coupled with permafrost in the ground might suggest that cold water could pool in the surface soil and resist evaporation for a short time, and might support the watering of high latitude type trees from Earth. But other challenges would keep the trees from making it.

I would say obviously that this would be the beginning of a transition to fluvial. Once the transition to fluvial began and if it progressed, I would divide teraform classifications into an Evaporative Fluvial, and Pooling Fluvial.

In an evaporative fluvial situation the ice in the northern hemisphere would tend to migrate to the southern hemisphere in the southern winter, and tend not to re-evaporate in the southern summer, because although there would be some melting of stray snowfalls at low latitudes on Mars, in the southern summer the ice deposites would tend to reflect sunlight back into space. So the southern ice cap would grow and the northern one shrink.

This would continue unless significant ice melt and large rivers were to emerge from the southern ice cap during summer, and that would happen only if the planet were warmed even more. Or using space mirrors to purposely melt the southern ice cap.

The reason I claim this is that most evaporation in that situation would be sublimation, and the northern ice cap being lower in elevation would experience a stronger greenhouse effect, but would still be prone to the evaporation of ice to atmospheric water vapors.

The plains of the the north would be favored for simple rugged life because even under those conditions the northern plains would be watered with snow packs in the winter. If the summers were warm enough to partially melt them before they evaporated/sublimated, then any thawed ground above the permafrost would help to retain water for a time. So, trees could be watered, but the conditions would likely be too harsh for them otherwise. But perhaps high arctic tundra of a sort would be possible over wide areas.
Lichens? The radiation flux might be moderated somewhat by then.

The Mariner Rift Valley would likely be arid, and unfavorable to life.

If this was maintained, and the atmosphere developed significant Oxygen and an Ozone layer, then perhaps some type of trees on the northern plains.

If the atmosphere were first inflated to a greater value, then I believe that sublimation would no longer be the dominant form of evaporation, and the northern plains would begin to flood with ice bound pools, that might become salty, that would depend on how much salt would leach out of the soils into the waters of the pools.

They would most efficiently accumulate water and retain it if most of the year the surface of the ice was frozen, but could melt at the peak warming times of the year, so that water pooling on the surface of the ice would bend and crack it. Once cracked, the melt water would flow downward into the cracks, inflating the ice. Any local streams of meltwater from snow packs around the pools would also contribute. This process would take energy into the lake, where it would be gaurded by the insulating layer of ice.

Solar energy can also pass through such ice and warm the waters in the summer, but the effect will not be as strong as it is here on Earth in Antarctic dry valley lakes.

If the atmospheric pressure were to rise to the degree that the southern ice cap could melt significantly in it's summers, then strong river systems would form in the southern hemisphere, with fresh water lakes, and finally at lower latitudes, salt lakes. This would begin to reverse the polarity of the water condensation, and so water evaporating from those lakes might begin to accumulate as condensate in the northern hemisphere, inflating a ocean in the northern hemisphere.

That is where I would have my preference to stop the process if possible.

As I see it an ideal would be a northern ocean with salt in it with an ice covering that only ruptures for a few weeks in the summer due to melt water pooling on it.

In Antarctica, I believe that if you drill a hole in such a body of water, Oxygen bubbles out. I suspect that this is because melt water brings CO2 into the lake and photo organisms using light through the ice extract Oxygen from it.

To me this indicates that the mixture of dissolved gasses in the water of such a lake/Ocean can be different than that of the atmosphere. So, you could extract Nitrogen from the atmosphere and inject it into the ocean and so perhaps make it more favorable to an expanded list of life forms. It is my intention that this ocean would be used to convert from a CO2 atmosphere to a more Oxygen dominated one. (Which would tend to be colder).

Perhaps some open water could be tolerated, but too much would poison the water with CO2, and would allow the Nitrogen to pass back into the atmosphere.

An ocean like that could serve as a carbon dump where organic materials would deposit to the bottom of it. Antarctic lakes tend to have low Oxygen in the bottom waters, and they tend to be warm maybe 20 degrees C. This might produce Methane, but organisms in the lake might digest that when it encounters Oxygen.

The Ocean if it inflated enough might flood the Mariner rift valley, and that could have some open water, being isolated from the other waters where you would want an elevated Nitrogen and Oxygen level.

Perhaps you could have underwater trees there. But that would require genetic engineering, and their leaf canopy would have to be just under the surface of the water. It would be frost free, and perhaps a source of wood. But It would really require some skills to modify trees for that.

So, with a Oxygen dominated atmosphere, and southern summers that are almost twice as long, and if at some locations the summer could have warm enough temperatures, and if the trees could tolerate low Nitrogen levels (Unless more is created/obtained), you might look for forests of high latitude trees in places in the southern hemisphere at mid latitudes. An of course in sheltered places at other locations.

I believe that trees need at least a few days at about 50 degrees F. But I did see an article claiming that there were some alpine trees that could tolerate a lesser situation for temperature. That was said to be on a mountain in Mexico.

Other vascular plants might endure better. Perhaps annuals in low Arctic and conditions resembling high latitudes on Earth.

Done.

Last edited by Void (2014-08-17 10:40:18)

undormant · 2014-08-26 04:36:58

A lot to think about there thanks.

R

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#1 2014-08-15 08:20:07

Effect of low gravity on plant life?

#2 2014-08-16 09:51:29

Re: Effect of low gravity on plant life?

#3 2014-08-16 16:58:44

Re: Effect of low gravity on plant life?

#4 2014-08-16 23:26:21

Re: Effect of low gravity on plant life?

#5 2014-08-17 07:48:34

Re: Effect of low gravity on plant life?

#6 2014-08-17 09:10:29

Re: Effect of low gravity on plant life?

#7 2014-08-17 09:45:44

Re: Effect of low gravity on plant life?

#8 2014-08-26 04:36:58

Re: Effect of low gravity on plant life?

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