How to grow plants in double normal CO2 ?
May 7, 2014 5:12 PM   Subscribe

Ideas for growing a plant, at home, in an artficially created atmosphere that has a lot more CO2 than normal - for a science project ?

My son is interested in an experiment that would attempt to grow a plant in atmosphere that had much more CO2 than is usual.

We don't have access to laboratory equipment.

Any ideas how CO2 could be produced and maintained in, perhaps, a Vivarium ? The quantities don't have to be exact so if we had one plant growing in normal atmosphere and one growing in "a lot more than normal CO2" that might be OK but the problem, as I see it, is : creating the CO2 and; ensuring the atmosphere is maintained over the course of the 4 weeks it would take to get a decent growth from whatever we grow.
posted by southof40 to Science & Nature (15 answers total) 1 user marked this as a favorite
You can buy containers of compressed CO2 for carbonating soda or beer pretty cheaply. Also paintball supply places have them. So buying CO2 isn't that hard.

Maintaining an atmosphere would be harder. Maybe a fish tank and a lot of duct tape? That sounds about right for a science fair project. Actually measuring CO2 concentration would require some equipment that's probably too expensive for a science fair project. If you have a valve and a supply tube maybe just give the plant tank a blast of CO2 every so often and see how it goes.
posted by GuyZero at 5:20 PM on May 7, 2014

It's hard to set up CO2 enrichment and leave it alone and have it stay enriched because in most ecosystems the rate of photosynthesis (removing CO2 from the air) is slightly higher than the rate of respiration (returning CO2 to the air).

Studies that do this in a lab setting have special growth chambers that monitor air chemistry and automated systems that add CO2 as needed. There are also field studies that do continuous CO2 enrichment. They truck it in and just keep blowing it on the plants. FACE (free air carbon dioxide enrichment) is the acronym used in the US for those studies--your son might enjoy reading about them.
posted by hydropsyche at 5:20 PM on May 7, 2014 [1 favorite]

Addressing the "creating of CO2" bit - aren't the carbonation cartridges from, like, soda stream machines and such filled with exactly that?
posted by EmpressCallipygos at 5:21 PM on May 7, 2014

CO2 can be bought in small cartridges for various hobbies (paintball, or charging selzer), or it can be bought in bottles such as are used by soda fountains-- the actual gas should be affordable and the bottle rented, maybe. Yellow pages for specialty gases.

He can build a clear tent around his plants and just blow CO2 into it on regular intervals. Something should stir the air, too, so that the air mixes. The tent doesn't need to be airtight, just substantial enough to resist mixing with regular atmosphere due to air currents in the room.

He could add dry ice, but supercold gas doesn't really want to mix with room-temperature gas, so it would sit like a sludge at the bottom of tent-- it needs to be up by the leaves, IIRC.

Not sure how best to test the air that's in the tent.
posted by Sunburnt at 5:21 PM on May 7, 2014

Please take a look at freshwater aquariums and CO2 use for plants. The systems are simple (gas, regulators) and not dreadfully expensive for a small set up. It makes a remarkable difference for aquatic and semiaquatic plants, so I think it might scale for your needs.
posted by halfbuckaroo at 5:30 PM on May 7, 2014 [1 favorite]

You may be able to find useful information by searching for information on planted freshwater fish tanks. They often use supplemental CO2, and there are various DIY schemes for producing it.
posted by madmethods at 5:31 PM on May 7, 2014

I really like halfbuckaroo's idea! I think CO2 enrichment in an aquatic system is much much more doable as a science fair project.
posted by hydropsyche at 5:35 PM on May 7, 2014

I did this science project as a kid. I raided the kitchen and used vinegar and baking soda to make C02.

So there's a way with stuff you already have in the kitchen, but it was awkward. The aquarium equipment designed for the task sounds better.
I used plastic soda bottles-cut-into-planters method to create a sealed atmosphere per plant. But in hindsight, my methodology was crap, so... use with caution :)
posted by anonymisc at 5:45 PM on May 7, 2014 [1 favorite]

I wrote a really long post but then thought of a much better and simpler idea.
  1. Buy some Arabidopsis thaliana seeds. Arabidopsis is the standard model plant in biology because they are cheap, easy to grow, and grow quickly. Using Arabidopsis will give you the benefit of a whole bunch of relevant literature (i.e. professional scientists have done this experiment before, and you might be able to read their papers to get ideas) plus it'll give the project some Real Science cachet.
  2. Sterilize them (you can find protocols online for this) and plant them in trays of sterile (i.e. baked) soil, evenly spaced. Two trays: one for your control group, one for your experimental group. (If you want to get really fancy you could grow them in agar between glass plates, so that you can see the roots.)
  3. Put your trays underneath some kind of transparent plastic box or tent, one that is not airtight. Set up your grow lights, thermometers, etc. In each container place a small styrofoam box with an open lid.
  4. Buy a bunch of dry ice. (Keep it in a cooler; you will still have to buy more every couple of days though, most likely.) As often as necessary, place a chunk of dry ice in your experimental group's styrofoam box. (You don't do anything with the control group's box, it's just there for standardization purposes.)
  5. Monitor plant growth by photographing both trays once a day at the same time of day.
posted by Scientist at 5:54 PM on May 7, 2014 [5 favorites]

Creating CO2 is pretty easy. Two possibilities that come to mind:

1) Mixing an acid with a carbonate yields CO2; the classic example is vinegar and bicarbonate of soda (baking soda in the US, I think).

2) CO2 is a waste gas from respiration. Mix flour and water to roughly the consistency of cream, and add some baker's yeast (fresh or freeze-dried, shouldn't make a difference). The bubbles formed are CO2. When the bubbling slows or stops, throw half the mixture away and replace with fresh flour and water. This will go faster at about 37 degrees centigrade, but room temperature is fine.

NB: for both the methods above, you can capture the gas by doing something like this, probably with plastic soda bottles and drinking straws. Note that this isn't perfect, as some of the CO2 will dissolve into the water and be wasted; you might want to just pipe it directly into e.g. a plastic sandwich bag instead, with no water trap. By marking the water level on the bottle (or measuring how inflated the bag is, perhaps by weight or using Archimedes' principle), you can deliver consistent amounts of CO2.

You can also buy CO2 quite easily. The posts above describe carbonation cylinders, which are almost certainly the most practical solution for your purposes.

Dry ice is solid CO2 and, left at room temperature, will change to gas. Some grocery or ice-cream shops will sell it, and some online food retailers will use it as a packing material, particularly for e.g. frozen fish. You can measure out a set weight, and capture it as above. However, it comes with important safety considerations. Firstly, dry ice is colder than -83C and can cause painful freeze injuries (effectively, frostbite). You can touch it for a second or two with bare skin, but only if your hands are COMPLETELY dry; otherwise, the moisture on your hands can freeze and act like a cement, holding the dry ice against you. Better to avoid touching it without tools or thick (and easily removed) rubber gloves. Eye protection is a good idea too, for the same reason. Secondly, NEVER put it in an airtight container: as it turns to gas, the pressure will rapidly climb and could cause the container to explode/burst. No flames or heat, but possibly shards of plastic and little bits of dry ice. This still applies when capturing the gas: you must have an easy route for excess gas to escape.

You're probably better off going for a pre-built setup as described above; I've just put these suggestions up in case you think they sound like a fun side-project.
posted by metaBugs at 5:55 PM on May 7, 2014 [1 favorite]

For a setup to get a cheap and relatively steady source of CO2 for about two weeks, look into building a yeast-powered CO2 rig. They are made out of soda bottles and aquarium tubing. Google "DIY CO2 planted tanks" for a gazillion articles on how to make one.

You could also do this with bottled CO2 (I use paintball tanks with regulators for my tanks) but the setup costs are expensive for a one-off project.

The difference in aquatic plants is huge, here's one of my tanks before CO2 injection, and after.
posted by jamaro at 6:09 PM on May 7, 2014 [2 favorites]

Simple combustion is a reliable method of creating an enriched CO2 environment. As a sub-sub contractor, I once simulated the CO2 concentrations of the space shuttle using pretty much all the big candles we had in the house in a small bathroom (6000 ppm in a 9x8x8 foot bathroom.

I suggest religious votive candles, with Jesus and the Virgin Mary on them. You will be able to compute how much water vapor and carbon dioxide they are creating by weighing them periodically and doing just a little chemistry. They burn for days at a time, and are inexpensive and reliable.

You will probably need a secondary enclosure to put the candle and vivarium into, and you will need to be a little clever to ensure good mixing and hence good CO2 distribution in the secondary container, and hence in the vivarium. A large cardboard box should do it.

It would be best if you could beg or borrow a CO2 analyzer, but you can probably work out a convincing CO2 concentration based on the elevation of temperature of the secondary container above ambient, and the burn rate of the candles. A chemical measure of CO2 concentration might be possible by titrating a water sample left to equilibriate in the secondary container (maybe many identical samples in small identical jars).
posted by the Real Dan at 7:30 PM on May 7, 2014 [1 favorite]

Nthing diy with coke bottles and yeast. We do this all the time with aquariums. Yeast, sugar and water in the bottle, hole in the lid with airline tubing, run into a fake greenhouse made of coat hangers and cling wrap. Control is greenhouse without the co2.
posted by smoke at 8:08 PM on May 7, 2014

Keep in mind that getting CO2 from burning candles or dry ice will also heat or cool the CO2-enriched air, adding another difference between the plants in it and the control plants. Who knows if any differences you might see would be from the CO2 concentration or from the temperature. Similarly, you'd probably want to put both sets of plants in similar enclousures (although one without added CO2) to eliminate any differences in greenhouse-type heat, drafts, blocked light, etc…
posted by JiBB at 12:11 AM on May 8, 2014 [1 favorite]

Oddly enough, there was just a story about a similar research project on the news this morning. Here is the link to the paper, which may have some information about their experimental setup.
posted by backseatpilot at 5:26 AM on May 8, 2014

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