Plant growth in Mars-like atmospheres


#1

Back in 2016 I did some research into what gas combinations we could use for growing plants in chamber on Mars
https://drive.google.com/file/d/16A_QnIHiIilqtgSBEvP6e9iaxBB4vsW0/view?usp=sharing

The final composition I settled on was “pure Martian air pressurised to 13.1 kPa, supplemented with O2 to give a total pressure of 34.5 kPa and an oxygen partial pressure of 21.4 kPa”

This thread was spun-off from the Science guest suggestion thread, so quoting previous comments here for context:

You totally just pointed out a major flaw in my research - I never accounted for the partial pressure of water vapor. Thanks!

I found a study that showed germination was possible under extremely high CO2.
T.N. McCaig, R.D. Hill, Cyanide-insensitive respiration in wheat: cultivar differences and effects of temperature, carbon dioxide, and oxygen, Canadian Journal of Botany. 55(1977) 549-55.

I didn’t really define what plants would be best, but a lot of my references used lettuce so that might be a safe bet.


#2

Great I’ll have some reading to do when I get some time!

Are you familiar with psycrometrics? Vapor pressure changes depending growth chamber design, and calculating the vapor pressure from the temperature and relative humidity can be pretty involved. I can try and find you some good resources to learn this if you need them.


#3

No, I’d love to learn though!


#4

Alright, for a basic introduction Dr. Kubota’s lecture is pretty much perfect:

And if you’re prepared to sift through some gnarly looking math, see if you can access (Elsevier has it):
Shallcross, D.C. Preparation of psychrometric charts for water vapour in Martian atmosphere. International Journal of Heat and Mass Transfer. Vol 48. p 1785–1796. Jan 2005.

One thing Kubota doesn’t make a big deal of is that most charts are specific to a certain pressure, and the vast majority are for Sea level (or near sea level) on Earth. Shallcross has some pretty epic charts designed specifically for plant chambers and HVAC on Mars, so he’s got charts for 10 kPa, 20 kPa, 50 kPa and 100 kPa.

So clearly, the thing we’re both interested in is Vapor Pressure, but Shallcross’s charts don’t actually have that, they’ve just got absolute humidity. I’m going to need to do some reading and stare at some equations to see if that easily converts to vapor pressure at pressures that aren’t ASL.

One thing I saw that I didn’t expect is that the capacity for air to hold water (kg of water)/(kg of air) rises pretty substantially as the pressure drops (a factor of 4-6 at 20 kPa). This means my initial guesses on vapor pressure could be wrong (by a lot). Although, I did read a medical study on subjects breathing pure O2 at 33% pressure that seemed to indicate that vapor pressure of water was equal regardless. So like I said, I’m going to have to stare at some math and I’ll get back to you.


And in case you’re interested:
Herlocher J.E., Quigley D.G., Behar V.S., et al. Physiologic response to increased oxygen partial pressure I: Clinical Observations. Aerospace Med. Vol. 35, No. 7., pg. 613–618. 1964. ( https://spacemedicineassociation.org/download/history/history_files_1964/35070613-1.pdf )


#5

Okay, I found the relationship between vapor pressure and absolute humidity. For an ideal gas it’s:
v = T * H / ( w/a + H )
where
v = vapor pressure,
T = total pressure
H = absolute humidity (kg of water/kg of atmosphere),
w = molecular weight of water = 18 g/mol
a = average molecular weight of the atmosphere (for earth, that’s 29 g/mol, for mars that’s ~43 g/mol)

So comparing 100 kPa to 20 kPa using Shallcross’s charts and also an ASL Earth chart:

T = 100 kPa, mars atmo
for 30 C @ 100% RH, H = .0188 kg/kg -> v = 4298 Pa
for 20 C @ 100% RH, H = .0102 kg/kg -> v = 2378 Pa
for 10 C @ 100% RH, H = .0054 kg/kg -> v = 1273 Pa

T = 20 kPa, mars atmo
for 30 C @ 100% RH, H = .113 kg/kg -> v = 4251 Pa
for 20 C @ 100% RH, H = .056 kg/kg -> v = 2360 Pa
for 10 C @ 100% RH, H = .028 kg/kg -> v = 1254 Pa

T = 101325 Pa, earth atmosphere
for 30 C @ 100% RH, H = .0275 kg/kg -> v = 4299 Pa
for 20 C @ 100% RH, H = .0148 kg/kg -> v = 2360 Pa
for 10 C @ 100% RH, H = .0078 kg/kg -> v = 1258 Pa

The difference between these sets is pretty small. Most of the error is probably from my having to eyeball the charts (with a small factor coming from these not being ideal gasses). It seems pretty clear that the water vapor pressure is dependent only on temperature . That’s consistent with what I thought I knew, so we’re all good there.

P.S.
RH = relative humidty


#6

Martian dirt makes good plant compost

Air quality greenhouse Arizona


#7

Heh, I’ve got a comment on that first video from 2 years ago.


#8

This might be a stupid question but have people just tried to replicate the atmospheric pressure at Earth levels with the Martian consistency and tried to breed plants while slowly reducing the atmospheric pressure generation over generation to see if it affected their growth versus plants that were same generation from Earth grown in the same lower pressure? Giving nature is our best Gene modifier.


#9

Sounds like an experiment in “artificial selection” involving corn I read about in introductory genetics.

The axis on the bottom is in generations… basically it took 70 years to move the strain from 4.6% oil to nearly 0%, or from 4.6% to 19%. That’s a long time to wait. The principal is sound though.

P.S.
I love that little spike at 40 generations… I’m guessing the Dust Bowl blew in and pollen from other fields “fixed” the oil deficiency for 1 generation.


Dudley, J.W. 1977. 76 generations of selection for oil and protein percentage in maize. In: Pollack, E., Kempthrone, O., and Bailey, T. (eds.) Proceedings of the International Conference on Quantitative Genetics, pp. 459-73. Ames: Iowa State Univ. Press.


#10

Well if we start now we might actually have results by the time we need to get someone to Mars :wink: I wonder if we could use a higher turnover rate of plant something that grows quickly and goes to seed quicker than corn. Would soy beans be test I’m going to have to look up to see what to do growth time on soybeans are but I was thinking they were pretty quick at least compared to corn. Was the corn experiment done in a controlled environment or was that done with like fields of corn out in the natural waiting for Seasons to change and all that.


#11

The corn experiment started in 1890ish and continued for at least 80 years (It might still be going, I’m not sure). That was before greenhouses were big, so it is probably all field work (I haven’t read the original study).

Absolutely, you could do this faster with a plant that grew faster or with a growth chamber where you could turn out 4 crops a year.

Really though, Genetic Engineering is an amazing short cut in this process. We’re understanding more and more what genes actually do and how we can efficiently manipulate the internal machinery of cells. We’ve actually been able to visualize the nanoscopic structure of these machines in a lot of cases. There’s literally a machine made of proteins in all living cells which rotates to generate power (like an engine).

We know exactly where these proteins are manufactured and what causes their production to be increased or decreased. It’s really amazing.


#12

Oh I have no doubt that our understanding of genetically engineering when it comes to plants is amazing I’m just wondering could we beat nature over short-term in control controlled conditions. If I go in and say Hey I want a corn plant that will grow in this light spectrum with this much light per year lower and can tolerate gas levels of XYZ what a lab be able to pump me out something faster than putting them inside greenhouses and just pumping the same gases in and doing the same experiment like they did with the corn


#13

Definitely yes. A GM lab would win that race. Then the populace would panic, and the government would make sure no one ever planted it. :slight_smile: (or so it seems like these days)


#14

Interesting now we just need bigger space station so we can have them do it in space and not have people panicking all we need to do is throw a label on there it’s for Mars and for science maybe not for science that could backfire. I wonder how much something like that would cost.


#15

Have you heard of Golden Rice? They took genes from bacteria and daffodils (whose yellow color comes from carotene) and put them into rice genome. The bodies of people who eat this rice process the carotene into Vitamin A which helps their eyes develop. It could reduce the incidence of blindness in the 3rd world by a staggering amount, but there’s lots of resistance from folks who don’t like GM.


#16

No I had not heard of that one that’s really cool and a great idea. But I did hear about the glow-in-the-dark cats used for AIDS research. Glowing cats shed light on Aids - BBC News


#17

What about using phytoplankton in a greenhouse on Mars to reduce CO2 levels they literally feed on co2 and nutrients. typically in fish tanks its waste products but I’m sure they can come up with a suitable substitute. That way your plants would get below the CO2 toxicity level and phytoplankton is low mass.


#18

Yeah I’ve got a link (more of a citation really) for that one:

Verseux C. et al. Sustainable life support on Mars – the potential roles of cyanobacteria. International Journal of Astrobiology. 15 (1): 65–92 (2016) doi:10.1017/S147355041500021X. Cambridge University Press. August 3, 2016.

The research is still super underdeveloped, but there are people working on it.


#19

I studied GM and i love the tech, However, I am against GM… Why?

Its not the tech and the results of the tech. Its the unscrupulous companies that work in GM. They create “products” and policies that are monopolistic and anti competition. They go after small farmers that “accidentally” gets pollinated with the GM genes and puts them out of business. they go after the Poor farmers that cant afford the GM crops and muscle them out with “pushing”(more like bribing) Governments to implement policies that make it hard for the little guys.


#20

I don’t understand how that could possibly get through a court… If you made no attempt to prevent the proliferation of your product (the genetic code of pollen in this case), that’s the legal definition of giving up your copy rights. They basically published source code when the flowers grew. That kind of thing is definitely predatory and should have been killed by the judicial system.

Edit: It’s like a malware writer suing people for using his software.