CO2 Carbon Dioxide supplementation

[daddydoall]

Wonder if anyone with knowledge, expertise, or experience have thoughts / experience with CO2 supplementation. Recent article in latest AOS magazine suggests benefit in sealed greenhouse in Winter. My understanding of CAM (crassulacean acid metabolism) is that plants like orchids (and tillandsia, cacti etc) respire (uptake CO2 and release O2) only when STOMA are open which is usually at night(They hold their breath all day). In C3 metabolism found in common plants CO2 markedly enhances growth when plants are warm and growing (this is why it is commonly used in indoor pot farms). But what of C4 plants? Seems to me it would make sense to burn a candle or alcohol burner in a sealed GH in the evening when the GH vents are typically closed and orchids are respiring (the article suggested in daytime) if at all and only if it is warm enough and bright enough that plants are growing. I would expect less benefit in the winter in an unheated GH as the benefit of supplemental CO2 is strongly temperature dependent at least in common C3 plants. So maybe I'll light a 6hr votive candle each evening in my GH to supply extra CO2? Of course this will hardly be an experiment since I only have one GH. Hence this thread.
Happy growing!

[estación seca]

There are a lot of issues to discuss. The bottom line is that CO2 supplementation does not help succulents in families like Cactaceae and Crassulacea, with CAM metabolism.

The second point is that flames in closed spaces produce carbon monoxide, CO, which poisons plants, just as it poisons animals. Don't do it. CO2 supplementation is done by supplying CO2 gas from a cylinder. You can get this at a restaurant supply house. CO2 is used in soda dispensing machines.

Succulents begin absorbing CO2 when pores open at night. But, there is a limit to how much CO2 they can absorb. As they bind CO2, by generating crassulacean acid (C4), the pH drops in the plant. At some point the pH drops far enough that the enzymes stop functioning. For cacti this is almost always well before midnight. This is one of the reasons cacti produce less plant mass per unit of growing time than many other groups of plants.

The following morning, with sunlight, the plant uses up its stored CO2. This is almost always complete by noon.

This daily pH switch can be tasted! Cactus flesh is very sour after midnight. By noon it is much less sour.

The limiting factor is not how much CO2 is available, but the pH inside the plant. So CO2 supplementation does not help plants with succulent metabolism, like many orchids.

Interestingly, DNA coding for CAM metabolic enzymes is found in almost all plants, including the most ancient studied to date. These genes are no longer activated in most terrestrial plants, only in succulents.

It is though CAM metabolism evolved to deal with low CO2 levels in ancient aquatic environments, and was later retrofitted by succulents to deal with low water availability.

[Ray]

Carbon dioxide cylinders may also be obtained from welding supply houses....

That cyclic pH swing occurs in orchids, too, and while I have not done the "taste test" to confirm it, measuring the pH of the reservoir in an S/H pot will do so.

A candle in a greenhouse isn't likely to produce much CO, unless it has been burning for a long time, and that greenhouse is REALLY well sealed. It will not, however, do diddley to enhance plant growth.

The global atmospheric carbon dioxide level is around 400 ppm at this point, but it takes three to four times that for plants to demonstrate significant enhanced growth. Go much beyond that, and it becomes toxic...

[daddydoall]

AOS publishing that article was irresponsible! Thanks for the accurate information!

[estación seca]

There's so much misinformation out there, but every minute spent crusading is a minute away from gardening.

[Optimist]

If you are going to try that experiment, then perhaps the bottle of yeast will be better than a lit candle?

Just fill a bottle of water with a pinch of bread yeast (a small amount or you will create a volcano,) and a little sugar, and put a balloon over the top with a tiny pin hole in the top. This will allow built up CO2 gas to escape.

[estación seca]

Originally Posted by Optimist

If you are going to try that experiment, then perhaps the bottle of yeast will be better than a lit candle?

Just fill a bottle of water with a pinch of bread yeast (a small amount or you will create a volcano,) and a little sugar, and put a balloon over the top with a tiny pin hole in the top. This will allow built up CO2 gas to escape.

The amount produced like that is so low it wouldn't be detectable in the greenhouse gas.