Plant growth in Mars-like atmospheres


A few more awesome examples of cellular machinery…
motor protein myosin crawling on actin filiment, contracting a muscle:

motor protein kinesin, escorting a vesicle:

protein synthesis:

DNA synthesis:


@MiniStoj I gave your paper a read through here’s some thoughts:

Increased water use efficiency under high CO2 is a function of “stomatal closure”. The stomata sense that there is enough CO2 for consumption and so they close down a bit, this reduces the rate at which water escapes through the pores. C3 plants evolved in a time with higher CO2 concentrations, so nowadays, in order to get enough CO2 to function, they open their pores as wide as they can, causing them to transpire extra water. Basically, we’re not really seeing “improved” efficiency, we’re seeing a return to baseline. In fact, if the CO2 levels dropped below around 25 Pa, C3 plants would start to be unable to grow. This is because of “photorespiration”, where low concentration of CO2 causes O2 to take the place of CO2 in the photosynthesis process. This is much less energy efficient, and doesn’t directly result in sugars. Photorespiration halts at about 60-80 Pa, but you can still see increased growth beyond this level (which is why greenhouses do this).

Commercial greenhouses enrich with CO2 all the time, so it’s a well studied thing for them. Your use of FACE experiments is good, but the open environments will never reach the 120+ Pa pCO2 that closed greenhouses often do. Try doing a search in a library that includes the journal “Acta Horticulturae”, you should get lots more hits as well as articles about CO2 toxicity in plants. The citation you provided for wheat refers only to germination if I’m not mistaken. The CO2 toxicity symptoms (including reductions in yields) usually appear on fully developed plants, so it might not have shown up in some of your readings which focused on sprouting.

Greater mitochondrial respiratory capacity in an atmosphere that is 75 kPa O2 is probably because the ~100 kPa “pure” O2 was more toxic. High levels of O2 produce superoxides near the mitochondria. I’ll bet a 50 kPa O2 atmosphere does even better, because that’s the threshold where human O2 toxicity stops. It seems that the cell’s in-built antioxidant system can only handle so much O2.

Requirement 3 needs to be revisited, 25 kPa CO2 is sufficiently toxic to kill humans within 1 minute. Indeed, it’s so toxic that our physiology is able to detect its presence. A sudden acidification of the blood caused by inhaling such high concentrations will likely induce “a sense of dread” within a single breath. This is a big operational hazard. Imagine someone with a broken seal on their breathing mask, unknowingly taking a breath and then experiencing panic, possibly rendering them unable to correct the fault.

Heres some starting points, I haven’t read all of these, but they look like they should be helpful:

co2 induced stomatal closure:
Chater, C, et al. Elevated CO2-Induced Responses in Stomata Require ABA and ABA Signaling. Curr Biol. 2015 Oct 19; 25(20): 2709–2716. doi: [10.1016/j.cub.2015.09.013] ( Elevated CO2-Induced Responses in Stomata Require ABA and ABA Signaling )

CO2 enrichment:
Tremblay, N and Gosselin A. Effect of Carbon Dioxide Enrichment and Light. HortTechnology. Vol 8(4). Dec 1998. ( )

CO2 toxicity:
Ali, M.B., Hahn, E.J. and Paek, K.-Y. 2005. CO2-induced total phenolics in suspension cultures of Panax ginseng C.A. Mayer roots: role of antioxidants and enzymes. Plant Physiology and Biochemistry 43: 449-457. ( )

superoxides, aka reactive oxygen species:
Fenton L, Beck G, Djali S, Robinson M. Hypothermia induced by hyperbaric oxygen is not blocked by serotonin antagonists. Pharmacol Biochem Behav 1993; 44:357–364.

extreme high levels of co2:
Feinstein J.S. et al. Fear and panic in humans with bilateral amygdala damage. Nature Neuroscience volume 16, p270–272. 2013. ( Fear and panic in humans with bilateral amygdala damage )



@MiniStoj You know,… maybe we’re over thinking this. (or maybe it’s just me…)

We’ve been looking at this like its a static problem, but it’s dynamic. High levels of CO2 is a self correcting problem for plants. If your chamber starts with 12 kPA of CO2, and then you grow plants in it… a lot of the CO2 is going to become O2 and very quickly. Since you found that germination is unaffected by high CO2, by the time we have large plants the CO2 would all be gone.

So if we start by planting a tray of seed outside the growth chamber. and we insert the tray into a chamber which we then pressurize with, say… 20 kPa of local Mars atmosphere and 10 kPa of O2. In a few days/weeks the plants will consume the CO2 replacing it with O2 until the CO2 levels reach “optimum” growth levels (whatever those might be for the given plant). At that point is when we start renewing the CO2 and extracting O2. That way, with the exception of that first chamber full of O2, all the gas comes from local Mars atmosphere. In time, as we deplete O2 with machines (probably zeolite O2 concentrator) and the plants deplete the CO2 with photosynthesis, the trace amounts of N2 and Argon in the input stream will start to fill the chamber and we’ll build up a supply of inert gas (which could also be useful… though not so much for plants).

Of course we’re still left with the problem of finding optimum CO2 levels for plants. I’m having a hard time actually finding the research that says 1200-1500 ppm (120-150 Pa) is optimal for growth rate. I’m wondering if the greenhouse industry actually uses that number because it’s most economic (because CO2 is expensive and buildings are leaky). I’ll keep looking…


This is a super interesting idea. Seems like it would be fairly simple to replicate on Earth too, and get some measurements on how long it takes to deplete the CO2/raise the O2.

There’s a point where Rubisco (enzyme that catalyses carbon fixation) becomes saturated with CO2. Anything above this concentration won’t have any additional affect. I can’t find an exact number for this at the moment, though. Interestingly, plants are pretty smart - if they have extra CO2, they end up making less Rubisco, and use the nitrogen (building block of the Rubisco protein) savings elsewhere in the plant:

Rogers, A., Fischer, B.U., Bryant, J., Frehner, M., Blum, H., Raines, C.A. and Long, S.P. 1998. Acclimation of photosynthesis to elevated CO2 under low-nitrogen nutrition is affected by the capacity for assimilate utilization. Perennial ryegrass under free-air CO2 enrichment. Plant Physiology 118 : 683-689.


The relative humidity is easy to calculate if you know the partial pressures of the gasses involved.
RH -= 100*p_water/Psat_water
RH: relative humidity
p_water is the partial pressure of water
Psat_water is the saturation/vapor pressure of the water at the air temperature
|Temperature|Saturation Pressure|
|(°C) |(kPa)|
|0.020000 |0.61210|
|5.0200 |0.87379|
|10.020 |1.2298|
|15.020 |1.7080|
|20.020 |2.3422|
|25.020 |3.1737|
|30.020 |4.2518|
|35.020 |5.6352|
|40.020 |7.3928|


In the case of a hydroponics room the p_water can be estimated as saturation pressure of water at the temperature of the water in the hydroponics system. if the temperature of the water is the same as the air temperature than the RH will be around 100%


Growth chambers are a bit weird. Because (as long as there is light) the leaves are always transpiring, the vapor pressure of water will tend toward 100%. If the RH stayed at 100% transpiration would cease (the water in the plant would be unable to move to the air), so you have to use a mechanical system to actively remove it (usually cold plates which condense droplets from the air). Most growth chambers and greenhouses have sensors and controls that let you pick a set point for RH, depending on how much water you extract from the chamber. Really what researchers want to control though, is vapor pressure depression (VPD), which is the difference between saturation and absolute humidity. It’s this difference which determines how quickly plants transpire. That means for two chambers at different temperatures, you’d need to select different RH in order to have the same VPD.

For Lisa’s purposes, if she wants to account for vapor pressure, she’ll need to set a requirement for chamber temperature, and RH, (or rather she needs to set the VPD based off cultural practices for that particular plant) and then we can calculate the expected range of vapor pressures.

A VPD of about 600 Pa looks like a good guess. Then, at 16 C­° RH would be 66%, and at 20 C° it would be 73%. Respectively, the corresponding vapor pressures would be about 1210 Pa and 1717 Pa. These were numbers used to grow potatoes in one CO2 experiment I found.
Cao, W., T.W. Tibbitts, and R.M. Wheeler. Carbon Dioxide Interactions with Irradiance and Temperature in Potatoes. Adv. Space Res. Vol. 14, No. 11. pp. 243-250. 1994.

Meanwhile, I know from experience that tomatoes like much higher temperatures and relative humidities, so the vapor pressure in a chamber growing them would be higher.

I found this site a while ago for calculating a saturation curve from temperature (it’s pretty hairy math):

Here’s an example:

Goff Gratch equation
(Smithsonian Tables, 1984, after Goff and Gratch, 1946):

Log10 ew =  -7.90298 (373.16/T-1)
                    + 5.02808 Log10(373.16/T)
                    - 1.3816 10-7 (1011.344 (1-T/373.16)  -1)
                   + 8.1328 10-3 (10-3.49149 (373.16/T-1)  -1)
                   + Log10(1013.246)
with T in [K] and ew in [hPa]

I’m hoping to find something nicer in Shallcross’s other works (apparently he wrote the book on this):
D.C. Shallcross, Handbook of Psychrometric Charts, Chapman and Hall, London, 1997.


I notice Rogers exclusively used NH4 as his N source. (nevermind, upon closer examination, there’s a typo NH4HO3, should be NH4NO3, :eyeroll:)… Still the rest of this might hold, I haven’t yet seen if he measured soil NO3:
I’ve read that high CO2 shifts plants’ ability to uptake N from reduced vs non reduced sources, i.e. NH4+ and NO3-. This is because plants have come to rely upon photorespiration as a method for converting one form of N to the other. As CO2 increase and photorespiration drops, the ability to uptake N can drop as well (depending on species and soil content). If his low-N group was using lots of NO3 from soil, then the shift upon CO2 enhancement would be more dramatic in this group. I wonder if that was relevant to his results.

… I still need to read through it all and think on it a bit.
Okay, finished reading Rogers. It looks like even if my theory is true, it doesn’t affect his conclusions. Although, it is possible that it magnified the effect of enhanced CO2 at low N in his data. Some soil analysis before samples were taken would have quantified soil NO3 content (and whether any microbial action was interconverting N sources). That may have let us gauge if photorespiration was at play in N uptake. Oh well, decades too late now!


If you’re proposing an experiment, I’d happily participate. Does TMRO have a budget for this? :wink:


If not we could probably raise the funds for it. put it next to the fish tank on the set. :rofl:


Finally! Ray Wheeler to the rescue… btw, great guest if you can get him.
Tested 50, 100, 200, and 500 Pa pCO2: found 100 Pa optimal for soybean.
That was way harder than it should have been.

He also talks about CO2 toxicity:

At 80 DAP [days after planting], some intervenal chlorosis was apparent on upper canopy leaves of both cultivars from the 500 Pa treatment. At harvest (90 DAP), some leaves from the 500 Pa treatment showed bleached, necrotic areas, which were not seen during the normal senescence of leaves in the other CO2 treatments.

Wheeler, R.M. C.L. Mackowiak, L.M. Siegriest, and J.C. Sager. Supraoptimal carbon dioxide effects on growth of soybean [Glycine max (L.) Merr.]. J. Plant Physiol. 142:173-178. 1993.


Has anybody looked into fruit and nut proucing trees along these lines … properbly pruned etc they could supply some essential vitamins and proteins


I saw an “Aspen FACE” paper (but I lost the citation) that enriched to around 60-80 kPa on non-windy days. They said the trees grew faster, the leaves were ~30% bigger (stomata were farther apart and less of them), the nuts were 50% to 80% bigger. Nutrient density went down slightly, with more fibrous content, but it was still decently nutritious.

The problem on Mars would be making a building big enough for a tree. An easier source of proteins and oils is soybean or peanut. There’s lots of good sources of vit A and vit C from shorter vegetable plants too. Still, maybe if the tree can be dwarfed down to a 4 foot variety, like some apples can, it might be doable.


Oh wow, this is a handy feature of high CO2 levels:

If some kind of pest hops a ride to Mars, it would be easy to remove them without having to clear out a growth chamber entirely.

Of note, it looks like short durations of high CO2 may not injure some plants (durations were 28 hr or less):

No damage to fresh kidney bean leaves subjected to 60 % CO2 treatment was observed at any of the tested temperatures.


Here we go, found some good examples of CO2 damage in young seedlings:

So it looks like damage will be species dependent. We’re going to have to test them.
They also found that strawberry was hardly damaged at all. Maybe we could isolate the protective gene(s) and insert it(them) into other species?


In commercial greenhouses are located by power stations for hot water and they use waste CO2 gas to make the plants grow better. Tomato :tomato: pickers are exposed to high CO2 levels, without any brain numbing.

Deep sea divers, underground miners have done lots of research on CO2.


OSHA limit for CO2 is 500 Pa. Greenhouses don’t usually get above 150 Pa.

Thresholds for symptom of CO2 toxicity in humans:
1000 Pa: No real symptoms (3-4 month exposure, submarine crews do this all the time)
2000 Pa: Slight acidosis of the blood begins (30 day exposure)
3320-4000 Pa: Discomfort, trouble breathing, acidosis of the blood, slight increase in respiration (after 3 days, metabolism changes can start the process of bone loss)
4650-5315 Pa: A feeling of heaviness, exercise problems, fast breathing, thinking impairment, sleep disorders (15 hour exposure)
6640 Pa: vertigo, headache, visual impairment, heavy breathing, heart problems, fast heart rate, high blood pressure, central nervous system problems begin (3-4 hour exposure)
8000 Pa: drastic worsening of symptoms, unable to exercise, mental performance impossible (1 hour exposure)
8000+ Pa: death is possible (depending on exposure duration)

for reference:
CO2 in expired air during normal breathing is about 5000-6000 Pa.
It could go as low as 4000 Pa during the rapid ventilation of exercise.

Workers in a growth chamber can wear breathing masks with scrubbers or an independent air supply to avoid these problems.

mostly from a chart from:
Barratt M.R. and Pool S.L. Eds. Principles of Clinical Medicine for Space Flight. New York: Springer; 2008. ( ISBN: 978-0-387-98842-9 )


Brain numbing = thinking impairment
See other topic in space health

also Submarines, aircraft, volcano gas monitors have lots of published paper and industry standards