CO2 Enrichment

[OzPhal]

Hi everybody,

I've read a range of articles about methods people have employed to accelerate growth rates of orchids through CO2 enrichment... I'm a microbiologist and during the course of my work i regularly culture anaerobic organisms - these organisms grow in the presence of high concentrations of CO2. One of the products that I use for this process are little CO2 generating sachets... they're rated for a 2.5L vessel and deliver a final CO2 concentration of approximately 6% CO2 and a final O2 concentration of approximately 15%. What are peoples thoughts on giving these a go for orchid growth? Obviously unless the vessel is completely sealed the CO2 concentration would decrease over time but it would give them a higher concentration than they would otherwise receive under normal conditions. I thought one of these thrown in a covered propagating tray would be an interesting experiment... any thoughts?

[Discus]

I seem to vaguely recall there was another CO2 enrichment thread within the last year - people have tried this with orchids - I think one member (perhaps Ray?) tried it in his greenhouse and couldn't discern an improvement.

One thing I seem to recall coming out of that discussion is that as most orchids are CAM or C4 plants; they already take advantage of higher nocturnal CO2 concentrations, so bumping it up a bit more, or giving it to them in the day, didn't have much effect.

Another thought is that orchid metabolism (growth certainly is) appears to be generally slow anyway, so may well not be limited by CO2.

Still, if you have enough sample orchids to conduct a well controlled trial, it might be fun

[Ray]

I didn't see any enhancement in the greenhouse, but that might have been a dosing issue.

The normal level of CO2 is 300-400 ppm, and if I recall, the upper limit is about 1500 ppm, with it becoming toxic at higher levels. 6% is 6000 ppm, and would likely kill the plants.

[tucker85]

I don't know if CO2 would make any difference. I'm not sure that orchids are capable of accelerated growth like some other plants. I used a CO2 injection system in a planted aquarium for a few years and the plants grew much faster but the availability of carbon dioxide in water is lower to start with. It would be an interesting experiment. The best setting to try it in would be a terrarium. If you do it, be sure to let us know how it goes.

[camille1585]

I had a look in scientific databases, and I found articles that do show that Phalaenopsis growth can be enhanced by adding more CO2.
One paper from 2008 (Aspects of CO2 Uptake in the Crassulacean Acid Metabolism Orchid Phalaenopsis) was particularily interesting. Their main findings were:
*CO2 uptake at night varies with temperature, and optimal uptake was at 20°C (uptake decreased as temps varied in either direction)
*At night CO2 absorption increased in proportion to CO2 concentration.
* Uptake is also possible in late afternoon, but high CO2 reduced somatal conductance.
*higher relative humidity (70% or more) was likely the most important factor for high CO2 absorption in Phalaenopsis.

As to the CO2 concentrations, here is what they say: "CO2 enrichment has been a major interest of Phalaenopsis growers to promote growth and the utility is well known. CO2 concentration affected the absorption in Phase 1 (at night). CO2 uptake increased significantly as the ambient CO2 concentration increased to 1500 ppm. At 500 ppm, CO2 absorption continued to increase for about 13 hours and then plateaued. However, at 1000 or 1500 ppm, the absorption continued to increase for more than 13 hours before leveling off"

From what I read elsewhere, the 'standard' CO2 levels applied to Phals (at night only) is between 700-1000ppm. I think the levels you talk about are far, far too high!!

So if all of this is true, you need to apply CO2 only at night, under high humidity, and at 20°C.

I hope I didn't bore anyone to death with this scientific bla-bla.....

[Tsuchibuta]

I remember reading in a old book (from the 40's) I had bought at library book sale about orchid growing. In it, the book stated that in his greenhouse in the winter that he would build a small woodfire in a grill then put out the fire and cover the embers with the lid. This was of course done at night. Ultimately this was to heat the greenhouse, but he remarked that he noticed increased growth in his plants after doing so. The author believe it to be because of increased CO2 as a byproduct of the wood fire. Perhaps the author wasn't mistaken, if he did this at night and increased CO2 levels perhaps the plants responded accordingly.


I always wanted to try it myself, but was afraid I would burn down my house, and wondered how much soot would buildup on the glass.

[Discus]

Of course, he needed to do an experiment to separate the effect of CO2 from the effect of a warmer environment (= faster metabolism & growth).

[camille1585]

Originally Posted by Discus

Of course, he needed to do an experiment to separate the effect of CO2 from the effect of a warmer environment (= faster metabolism & growth).

I read that higher light and temps during the day enhance CO2 uptake at night. But if you're talking about night temps then higher temps is actually counterproductive. In the article I cited they found that uptake was low at 25°C, and non existant at 30°C.

[OzPhal]

Originally Posted by Ray

I didn't see any enhancement in the greenhouse, but that might have been a dosing issue.

The normal level of CO2 is 300-400 ppm, and if I recall, the upper limit is about 1500 ppm, with it becoming toxic at higher levels. 6% is 6000 ppm, and would likely kill the plants.

Thanks Ray for your input - 6% is 60,000ppm - theoretically you could proportionally increase the volume of the growth cabinet to reduce the ppm to the non-toxic range i guess...

[OzPhal]

Originally Posted by camille1585

I read that higher light and temps during the day enhance CO2 uptake at night. But if you're talking about night temps then higher temps is actually counterproductive. In the article I cited they found that uptake was low at 25°C, and non existant at 30°C.

This is very interesting! i can see an experiment brewing here

So, in theory, if i provided a terrarium of approximately 100L volume (to give a final CO2 concentration of approximately 0.15%), 20oC at night with high humidity and warmer temperatures with high humidity during the day then that should be the 'ideal' conditions... It would be fairly easy to run a control too - simply a 100L terrarium with no CO2 enrichment! You could theoretically use a flask and break the flask in two community pots so that your sample size is larger rather than using one plant in each. Growth would have to be measured by two parameters - plant weight and the plants physical growth