The facts about CO2 ppm: don't use 1,500!

guineapig said:

Yes this is a very informative thread on co2....

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You're very welcome. And thank you for being a mod, I know it's sometimes thankless and probably a PITA, like separating kids in a sand box.

guineapig said:

I was always skeptical of many things I had read about CO2, they seemed to lack data...
I had always read that you can a CO2 supplemented plant can thrive even when temps
reach into the mid-90s, but that never made much sense to me....

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Me either.

guineapig said:

So there is never any good reason to go past 1000-1100 ppm?

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1,200 ppm is okay to use, but I worry about the effect of 1,200 ppm on Rubisco activase. Mostly because even with automated "fuzzy logic" CO2 tank systems, the CO2 fluxes quite a bit, especially after the 'night'. Also, from most of the academic lit. I have read on CO2 saturation, about 1,000 ppm seems to be the sweet spot. Up to 1,200 ppm can offer benefits, but the difference between 1,000 ppm and 1,200 ppm isn't huge; unlike the difference between 350 ppm and 1,000 or 1,200 ppm.

Because the CO2 level fluxes, often as much as 100-200 ppm even with top of the line fuzzy logic control (IME), I set my CO2 controller (CHHC-4) to either 900 or 1,000 ppm.

guineapig said:

(After we talk CO2 I hope we can talk O2 in the rhizosphere)

kind regards from guineapig

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What do you want to talk about with respect to O2?

pezmasterelite said:

Hello,

I am interested in seeing these full articles. I am having a little hard time finding access to these things as I am not at a university anymore.

Thanks

pez

EDIT: I was able to find "Very high CO2 Reduces Photosynthesis, Dark Respiraion, and Yield in Wheat", here

http://aob.oxfordjournals.org/content/80/4/539.full.pdf

I would like to see "Super-optimal CO2 reduces wheat yield in growth chamber and greenhouse environments" if possible.

Thanks again.

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Sure, but I don't have it here. I read it, took a few notes, and didn't bring it home. I'll have to go back to the bio library, and I am going there tomorrow anyway. I'll try to get it for you tomorrow.

would a side by side test prove anything?

CO2 on at 900, off at 1100 @80 degrees F.
CO2 on at 1300 off at 1500 @80 degrees F.

In what regard? And testing what?

The science of CO2 use by C3 plants is pretty well understood, at least the low hanging fruit such as this thread topic. I don't see much room for disagreement about the benefits (or lack thereof) from 1,500 ppm; but science can prove itself wrong, so I'd be interested.

The problem with such testing, especially with a gas, is proper study design and controls. Without a grow space with needed equipment, which is at least ~$2,000 for a small space, not including tools to measure effect of CO2, I don't think much useful info can be gained from a side by side.

The problem with most side by sides is the main determining factor of which side is 'better' is subjective ratings from people. Ex., "bigger buds", "more growth", "greener", "better high", etc.; all of those are subjective and not analytically (unbiased) measured. It's been proven by various studies, that even if researchers try to be unbiased, they are still biased, so results and conclusions must be based on quantifiable (at least objectively qualifiable) measurements.

That said, I have tested 1,500 ppm vs 1,000 ppm, (sadly) using subjective measurements, and found 1,000 ppm provided for better growth, yield and quality; at least the growth and quality of 1,000 ppm wasn't less than from 1,500 ppm. I was only testing for shits and giggles, I expected the results I found (which in and of itself is a big no-no in science ... ).

Other ICmag'ers have tested ~1,000 ppm vs 1,500 ppm after I wrote to them the gist of this thread. Maybe they will stop in and post their thoughts and experiences.

Good info again Spurr. I've never used CO2 but setting up a new room this Winter and if I go sealed you have saved me a lot of wasted CO2 and would now expect to see even better results!

Nitrate N, ammonium N and CO2 ...

There is a fairly large collection of studies looking at effects from long term (days/weeks/months) increased CO2 levels, on various plants and trees. There is not sufficient evidence to form an opinion yet, however, at this time it appears plants given only (or mostly) nitrate N benefit from increased CO2 for only a short time (days/weeks).

After some days/weeks of high CO2 ppm (ex., 800-1,000) it seems to be that the rate of photosynthesis and net rate of photosynthesis of plants given only NO3 (nitrate) drops down to levels similar to plants with ambient level of CO2 (~350 ppm). However, plants given considerable ammonium (NH4) in relation to NO3 didn't show (as great as) reduced rates of photosynthesis.

It seems to be that NO3 and/or NH4 affect the plant response to increased CO2, re photosynthesis, after some days/weeks. I am unsure of what might be happening, but I do know NH4 gets converted into amino acid (proteins) in the roots using sugar moved from source tissue (leafs/buds) to sink tissue (roots). And I know NO3 can either be converted into amino acid in roots, or moved to shoots/leafs and stay as NO3 and/or be converted into amino acid (and/or NH4?).

What that means is to play it safe, growers who supplement with CO2 should consider the NO3:NH4 ratio they use (if they're conventional growers). The NO3:NH4 ratio is very important for a few reasons, CO2 is not commonly considered among those reasons. In other words, the same ratio that may benefit use of CO2 by plants will benefit the plant in other ways (ex., greater pH balance in rhizosphere and root zone/water).

One consideration is the process of "nitrification", which is the microbial conversion of NH4 (and NH3, re ammonification) into NO2 and then finally NO3. What the means is for media with lots of microbes (esp "nitrifiers", i.e., nitrifying bacteria) much of the NH4 will be converted into NO3, and quite fast.

The ideal ratio of NO3:NH4 is 3 or 4. I like the latter, which is 80% NO3 and 20% NH4 out of total N (NO3 + NH4). In terms of pH the ideal ratio is 1, but that's too much NH4. In terms of CO2, I think at least a ratio of 10 should be used. I have used ratios 10, 13 and 15 in the past, they all function very well. This next grow I will be using a ratio of 4, with 128 ppm NO3 and 32 ppm NH4, from veg to harvest.

Note: There are important considerations when choosing to increase NH4, ex., canopy temperature and grow stage. The latter issue is about where most of the photosynthate 'goes' and is 'used'. For flowering plants it mostly stays in the flowers/leafs/bracts, i.e., locally. That means less sugar is available (to be translocated from leafs to roots) for conversion of NH4 into amino acids, in the roots.

spurr your wealth of knowledge is amazing! I always know when i see one of your posts it will be chock full of some badass info! thanks for your contributions!

@ all,

Thanks for the kind words, I'm glad this info is helpful. I really hope this info kills the 1,500 ppm myth sometime in the future. It bothers me to think about all the growers unknowingly providing toxic levels of CO2 for their plants (many growers use > 1,500 ppm!), thanks to bullshit claims from so-called cannabis "gurus".

Hi,

Not that I disagree with your findings, but I think high levels of CO2 will inhibit photorespiration, not increase it. This is due to the fact that the stomata will be less open due to excess CO2 in the inner leaf area. This is also why plants in high CO2 environments require less water as they do not transpire as much.

pez

Hey,

Plants naturally carryout photorespiration all the time, it's the rate that's important; higher rate = unhealthy plant. Photorespiration happens as a result of nitrate usage by plants, as well as a result from environmental stress, and plants will emit O2 from leafs as well as roots (just like CO2). High CO2 does reduce stomatal openness, but it doesn't close stoma, gasses still enter and exit. That is why ethylene is able to increase as CO2 increases, even though stomata are less open.

Hi,

I really hate to be a stickler, but my botany book says the opposite,

higher CO2 concentration inhibits phototranspiration.

Also, here is a link to a paper which seems to say the same thing.

http://www.pnas.org/content/101/31/11506.full

From the start of the second paragraph,

"Transferring C3 plants from ambient (≈360 μmol·mol-1) to elevated (≈720 μmol·mol-1) CO2 concentrations decreases photorespiration and initially stimulates net CO2 assimilation and growth by ≈30% (7)."

Also, I believe logically that if the stomata are less open they will have a harder time to transpire or respirate as much gas as if they were more open.

I really don't want to start an argument here, just trying to study up and determine how many typos are in my botany book, I have found some before.

Peace,

pez

Hi,

I am not sure, but I think the paper I linked answers some of the questions in your previous post about nitrogen use by plants.

It appears( from their conclusions ) the higher CO2 concentration inhibits the plants ability to move the NO2- to the chloroplasts to form NO3-. It does this by effecting the pH gradient and not allowing the molecules to move across the chloroplasts membranes.

Peace,

pez

Hey,

Trust me, you're not starting an argument. If I'm wrong about something I like to know, I would never get upset at someone who can show me I'm wrong; I would however thank them .

You could be correct, however, I think not. I will dig up what I can find with respect to photorespiration and CO2 at and above saturation point > 1,000 ppm. My point was that high CO2, especially > 1,200 ppm, can increase photorespiration. I'm not sure by what you cited it shows the effects from super-optimal CO2 levels we are discussing, i.e., > 1,200 ppm.

I will read that study soon, thanks. I will also double check my refs to make sure I'm not making shit up

Thanks ! Great post!

Been running perpetual at 800 or so ! Knew I was forgetting something .......the ethylene !

pezmasterelite said:

Hi,

I am not sure, but I think the paper I linked answers some of the questions in your previous post about nitrogen use by plants.

It appears( from their conclusions ) the higher CO2 concentration inhibits the plants ability to move the NO2- to the chloroplasts to form NO3-. It does this by effecting the pH gradient and not allowing the molecules to move across the chloroplasts membranes.

Peace,

pez

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Interesting, thanks. I will read up for sure.

Spurr,

Does barometric pressure play a role in a plant's growth and ability to photosynthesize? I read somewhere that grow rooms with intake fans that are more powerful than exhaust fans will create excess pressure in the grow environment which can be problematic.

Thanks,

b_d

thanks for all they great info.

I have a question about the day night co2 levels. I run 2 sealed rooms on a flip flop that are constantly exchanging air with eachother. I do this for cooling purposes, each side has a minisplit that the lights off room helps cool the lights on room. Plants are currently getting co2 24/7 at 1500 ppms. Has been working great for me so far. But if I can make the plants happier, im all ears.

With my setup what would you suggest I set my co2 at to balance out the good/bad? If you could choose only 1 ppm setting for day/night what would it be?


Thanks

Sick thread as always spur. thought you might like this:

btw i peak at 1200, not 1500. But otherwise i like the chart.

i heard somewhere (i think the seemorebuds dvds) that you should match your nutrient ppms to your co2 ppms. so, technically where people peek at 1200 ppms and gradually taper down... it makes sense.

if your temp is lower maybe you don't need as much CO2?