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

High,

I haven't posted much lately, but I thought this topic was important enough to write a thread. I have written about this topic quite a lot in the past, but I have never made a thread just for this topic.

My goal: to try and kill the myth that 1,500 ppm CO2 is ideal. I want to get it known in the cannabis world, that it's important to not use > ~1,100-1,200 ppm CO2.

In short, the claim that 1,500 ppm CO2 is ideal for cannabis is total hogwash. I challenged anyone a while ago to find a single scientific study showing 1,500 ppm is ideal for C3 flowering plants, or even just to find the reasons why it's claimed 1,500 ppm is ideal in the cannabis world. I assume the myth (yet another!) came from the liked of Ed Rosenthall or George Cervantes or Mel Frank, etc.

If there is interest in the 'whys' I can explain why it's important to not use > 1,200 ppm, ideally we would use ~1,000-1,100 ppm. The effects from "super-optimal" CO2 concentrations range from reduced rate of photosynthesis, to reduced yield, reduced root growth, reduced stomatal openness, increased photorespiration, etc. In other words, nothing good.

The reason why we should ideally use ~1,000 ppm, is for most C3 species (and C4 I think), CO2 "saturation" occurs at ~1,000-1,100 ppm. That means more than ~1,100 ppm (up to 1,200 ppm) isn't going to help the plants, it's only going to waste CO2 and hinder plants if CO2 is about > 1,200 ppm.

The reason why we should ideally use < 1,200 ppm CO2 is the effect high (super-optimal) CO2 has on "Rubisco activase", the substance that turns inactive "Rubisco" into active Rubsico. At CO2 > ~1,200 (and temp > ~89'F) Rubsico activase is inhibited, which in turn inhibits conversion of inactive Rubisco into active Rubisco. And active Rubisco is needed for high rate of photosynthesis, which in turn leads to high growth rates and high yield, etc.

So, to sum up: It's important to keep CO2 below ~1,200, and to be safe and most efficient, keep CO2 at ~1,000 ppm. Night time CO2 should be < ~500 ppm, unless one is trying to reduce dark respiration and stretch, then upwards of 750 ppm can be used for short periods (otherwise leaf chlorosis can set in).

I can fully cite all those claims, if anyone wants to read the academic lit. For now, here are a few good studies looking at C3 wheat and rice plants:

• Note: 0.0001% CO2 = 1 ppm CO2 = 1 micromole mol^-1 CO2 (mol^-1 is written as "mol-1" below)

CO2 crop growth enhancement and toxicity in wheat and rice
Bugbee B, Spanarkel B, Johnson S, Monje O, Koerner G.
Adv Space Res. 1994 Nov;14(11):257-67.

Abstract

The effects of elevated CO2 on plant growth are reviewed and the implications for crop yields in regenerative systems are discussed. There is considerable theoretical and experimental evidence indicating that the beneficial effects of CO2 are saturated at about 0.12% CO2 in air. However, CO2 can easily rise above 1% of the total gas in a closed system, and we have thus studied continuous exposure to CO2 levels as high as 2%. Elevating CO2 from 340 to 1200 micromoles mol-1 can increase the seed yield of wheat and rice by 30 to 40%; unfortunately, further CO2 elevation to 2500 micromoles mol-1 (0.25%) has consistently reduced yield by 25% compared to plants grown at 1200 micromoles mol-1; fortunately, there was only an additional 10% decrease in yield as the CO2 level was further elevated to 2% (20,000 micromoles mol-1). Yield increases in both rice and wheat were primarily the result of increased number of heads per m2, with minor effects on seed number per head and seed size. Yield increases were greatest in the highest photosynthetic photon flux. We used photosynthetic gas exchange to analyze CO2 effects on radiation interception, canopy quantum yield, and canopy carbon use efficiency. We were surprised to find that radiation interception during early growth was not improved by elevated CO2. As expected, CO2 increased quantum yield, but there was also a small increase in carbon use efficiency. Super-optimal CO2 levels did not reduce vegetative growth, but decreased seed set and thus yield. The reduced seed set is not visually apparent until final yield is measured. The physiological mechanism underlying CO2 toxicity is not yet known, but elevated CO2 levels (0.1 to 1% CO2) increase ethylene synthesis in some plants and ethylene is a potent inhibitor of seed set in wheat.

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Super-optimal CO2 reduces wheat yield in growth chamber and greenhouse environments
Grotenhuis T, Reuveni J, Bugbee B.
Adv Space Res. 1997;20(10):1901-4.

Abstract

Seven growth chamber trials (six replicate trials using 0.035, 0.12, and 0.25% CO2 in air and one trial using 0.12, 0.80, and 2.0% CO2 in air) and three replicate greenhouse trials (0.035, 0.10, 0.18, 0.26, 0.50, and 1.0% CO2 in air) compare the effects of super-optimal CO2 on the seed yield, harvest index, and vegetative growth rate of wheat (Triticum aestivum L. cvs. USU-Apogee and Veery-10). Plants in the growth chamber trials were grown hydroponically under fluorescent lamps, while the greenhouse trials were grown under sunlight and high pressure sodium lamps and in soilless media. Plants in the greenhouse trials responded similarly to those in the growth chamber trials; maximum yields occurred near 0.10 and 0.12% CO2 and decreased significantly thereafter. This research indicates that the toxic effects of elevated CO2 are not specific to only one environment and has important implications for the design of bio-regenerative life support systems in space, and for the future of terrestrial agriculture.

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Very high CO2 reduces photosynthesis, dark respiration and yield in wheat
Reuveni J, Bugbee B.
Ann Bot. 1997 Oct;80(4):539-46.

Abstract

Although terrestrial CO2 concentrations, [CO2] are not expected to reach 1000 micromoles mol-1 for many decades, CO2 levels in closed systems such as growth chambers and glasshouses, can easily exceed this concentration. CO2 levels in life support systems in space can exceed 10000 micromoles mol-1 (1%). Here we studied the effect of six CO2 concentrations, from ambient up to 10000 micromoles mol-1, on seed yield, growth and gas exchange of two wheat cultivars (USU-Apogee and Veery-l0). Elevating [CO2] from 350 to 1000 micromoles mol-1 increased seed yield (by 33%), vegetative biomass (by 25%) and number of heads m-2 (by 34%) of wheat plants. Elevation of [CO2] from 1000 to 10000 micromoles mol-1 decreased seed yield (by 37%), harvest index (by 14%), mass per seed (by 9%) and number of seeds per head (by 29%). This very high [CO2] had a negligible, non-significant effect on vegetative biomass, number of heads m-2 and seed mass per head. A sharp decrease in seed yield, harvest index and seeds per head occurred by elevating [CO2] from 1000 to 2600 micromoles mol-1. Further elevation of [CO2] from 2600 to 10000 micromoles mol-1 caused a further but smaller decrease. The effect of CO2 on both wheat cultivars was similar for all growth parameters. Similarly there were no differences in the response to high [CO2] between wheat grown hydroponically in growth chambers under fluorescent lights and those grown in soilless media in a glasshouse under sunlight and high pressure sodium lamps. There was no correlation between high [CO2] and ethylene production by flag leaves or by wheat heads. Therefore, the reduction in seed set in wheat plants is not mediated by ethylene. The photosynthetic rate of whole wheat plants was 8% lower and dark respiration of the wheat heads 25% lower when exposed to 2600 micromoles mol-1 CO2 compared to ambient [CO2]. It is concluded that the reduction in the seed set can be mainly explained by the reduction in the dark respiration in wheat heads, when most of the respiration is functional and is needed for seed development.

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Super-optimal CO2 reduces seed yield but not vegetative growth in wheat
Grotenhuis TP, Bugbee B.
Crop Sci. 1997 Jul-Aug;37:1215-22.

Abstract

Although terrestrial atmospheric CO2 levels will not reach 1000 micromoles mol-1 (0.1%) for decades, CO2 levels in growth chambers and greenhouses routinely exceed that concentration. CO2 levels in life support systems in space can exceed 10000 micromoles mol-1(1%). Numerous studies have examined CO2 effects up to 1000 micromoles mol-1, but biochemical measurements indicate that the beneficial effects of CO2 can continue beyond this concentration. We studied the effects of near-optimal (approximately 1200 micromoles mol-1) and super-optimal CO2 levels (2400 micromoles mol-1) on yield of two cultivars of hydroponically grown wheat (Triticum aestivum L.) in 12 trials in growth chambers. Increasing CO2 from sub-optimal to near-optimal (350-1200 micromoles mol-1) increased vegetative growth by 25% and seed yield by 15% in both cultivars. Yield increases were primarily the result of an increased number of heads per square meter. Further elevation of CO2 to 2500 micromoles mol-1 reduced seed yield by 22% (P < 0.001) in cv. Veery-10 and by 15% (P < 0.001) in cv. USU-Apogee. Super-optimal CO2 did not decrease the number of heads per square meter, but reduced seeds per head by 10% and mass per seed by 11%. The toxic effect of CO2 was similar over a range of light levels from half to full sunlight. Subsequent trials revealed that super-optimal CO2 during the interval between 2 wk before and after anthesis mimicked the effect of constant super-optimal CO2. Furthermore, near-optimal CO2 during the same interval mimicked the effect of constant near-optimal CO2. Nutrient concentration of leaves and heads was not affected by CO2. These results suggest that super-optimal CO2 inhibits some process that occurs near the time of seed set resulting in decreased seed set, seed mass, and yield.

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The Cliff Notes:

In all the studies above, and others I have read on C3 plants, ~1,200 ppm CO2 is the limit to benefits from CO2. And ~1,000-1,200 ppm CO2 is the saturation point for most C3 species. For reference: 1,200 ppm CO2 = 0.12% CO2 = 1,200 micromole mol^-1 CO2.

@ MODS: May I request this thread be made a stickey?

spurr said:

High,

I haven't posted much lately, but I thought this topic was important enough to write a thread. I have written about this topic quite a lot in the past, but I have never made a thread just for this topic.

My goal: to try and kill the myth that 1,500 ppm CO2 is ideal. I want to get it known in the cannabis world, that it's important to not use > ~1,100-1,200 ppm CO2.

In short, the claim that 1,500 ppm CO2 is ideal for cannabis is total hogwash. I challenged anyone a while ago to find a single scientific study showing 1,500 ppm is ideal for C3 flowering plants, or even just to find the reasons why it's claimed 1,500 ppm is ideal in the cannabis world. I assume the myth (yet another!) came from the liked of Ed Rosenthall or George Cervantes or Mel Frank, etc.

If there is interest in the 'whys' I can explain why it's important to not use > 1,200 ppm, ideally we would use ~1,000-1,100 ppm. The effects from "super-optimal" CO2 concentrations range from reduced rate of photosynthesis, to reduced yield, reduced root growth, reduced stomatal openness, increased photorespiration, etc. In other words, nothing good.

The reason why we should ideally use ~1,000 ppm, is for most C3 species (and C4 I think), CO2 "saturation" occurs at ~1,000-1,100 ppm. That means more than ~1,100 ppm (up to 1,200 ppm) isn't going to help the plants, it's only going to waste CO2 and hinder plants if CO2 is about > 1,200 ppm.

The reason why we should ideally use < 1,200 ppm CO2 is the effect high (super-optimal) CO2 has on "Rubisco activase", the substance that turns inactive "Rubisco" into active Rubsico. At CO2 > ~1,200 (and temp > ~92'F) Rubsico activase is inhibited, which in turn inhibits conversion of inactive Rubisco into active Rubisco. And active Rubisco is needed for high rate of photosynthesis, which in turn leads to high growth rates and high yield, etc.

So, to sum up: It's important to keep CO2 below ~1,200, and to be safe and most efficient, keep CO2 at ~1,000 ppm. Night time CO2 should be < ~500 ppm, unless one is trying to reduce dark respiration and stretch, then upwards of 750 ppm can be used for short periods (otherwise leaf chlorosis can set in).

I can fully cite all those claims, if anyone wants to read the academic lit. For now, here are a few good studies looking at C3 wheat and rice plants:

• Note: 0.0001% CO2 = 1 ppm CO2 = 1 micromole mol^-1 CO2 (mol^-1 is written as "mol-1" below)

CO2 crop growth enhancement and toxicity in wheat and rice
Bugbee B, Spanarkel B, Johnson S, Monje O, Koerner G.
Adv Space Res. 1994 Nov;14(11):257-67.

Super-optimal CO2 reduces wheat yield in growth chamber and greenhouse environments
Grotenhuis T, Reuveni J, Bugbee B.
Adv Space Res. 1997;20(10):1901-4.

Very high CO2 reduces photosynthesis, dark respiration and yield in wheat
Reuveni J, Bugbee B.
Ann Bot. 1997 Oct;80(4):539-46.

Super-optimal CO2 reduces seed yield but not vegetative growth in wheat
Grotenhuis TP, Bugbee B.
Crop Sci. 1997 Jul-Aug;37:1215-22.

Click to expand...

Hey Spur
I don`t post much but everytime I check out this site I end up reading your post. I just want to thank you for all your hard work and all the help you have given to many,many growers myself included TY
1969BUBBA

1969bubba said:

Hey Spur
I don`t post much but everytime I check out this site I end up reading your post. I just want to thank you for all your hard work and all the help you have given to many,many growers myself included TY
1969BUBBA

Click to expand...

Ditto on that one. thanks Spurr for coming out of hiding and giving us another gem. your scientific approach to everything is very refreshing in this paradigm and myth based "community"

my #1 mentor for sure, and thats with zero private lessons.

another great post . thanks for the info

Ethylene ...

A concern with high Co2, especially over ~1,000 ppm, is ethylene buildup. Even low ppm concentration of ethylene gas can affect flower (inflorescence) size, plant growth rate, seed set (for breeders), senescence, etc. If grow rooms or greenhouses are not vented at least once, ex., at the end of the day, and Co2 is used at 1,000 to 1,500 ppm (esp the latter), ethylene can buildup to levels that will lower yield.

Here are a few good resources:

"Ethylene synthesis and sensitivity in crop plants"
Stephen P. Klassen and Bruce Bugbee
HortScience Vol. 39(7) pp. 1546-1552 (2004)



"Ethylene In The Greenhouse"
The authors explain how to detect ethylene, how to take action against it and how to stop problems before they happen
By W. Roland Leatherwood and Neil S. Mattson
April 2010
http://www.greenhousegrower.com/magazine/?storyid=3153




"Ethylene, Plant Senescence and Abscission"
Stanley P. Burg
Plant Physiol. 1968 September; 43(9 Pt B): 1503–1511.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1087144/pdf/plntphys00512-0034.pdf

EDIT:

I just fixed a typo, I first wrote that Rubisco activase is hindered when canopy temps exceed just over 92'F, but that's wrong. The correct temp is just above 89'F. So, make sure not to let canopy temp exceed 89'F

Thanks for the info.

I might have missed it, but can you explain the connection between co2 over 1000 ppm and ethylene build-up?

@ 1969bubba, dizzlekush and supermanlives,

Thanks for the kind words, I'm glad you found this info useful.

Well done well presented . +rep

schwilly said:

Thanks for the info.

Click to expand...

You're very welcome.

schwilly said:

I might have missed it, but can you explain the connection between co2 over 1000 ppm and ethylene build-up?

Click to expand...

You didn't miss it, I neglected to go into detail, sorry. See these references I attached to this post:

Ethylene synthesis and sensitivity in crop plants
Stephen P. Klassen and Bruce Bugbee
HortScience Vol. 39(7) pp. 1546-1552 (2004)





Light inhibition of the conversion of 1-amino-cyclopropane-1-carboxylic acid to ethylene in leaves is mediated through carbon dioxide
Kao, C.H. and S.F. Yang
Planta 155:126-266 (1982)

• note: the the highest rate of ethylene release was at ~> 1,200 ppm (0.12%), with half max release at 600 ppm.

Abstract.

The mechanism of light-inhibited ethylene production in excised rice (Oryza sativa L.) and tobacco (Nicotiana tabacum L.) leaves was examined. In segments of rice leaves light substantially inhibited the endogenous ethylene production, but when CO2 was added into the incubation flask, the rate of endogenous ethylene production in the light increased markedly, to a level which was even higher than that produced in the dark. Carbon dioxide, however, had no appreciable effect of leaf segments incubated in the dark. The endogenous level of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, was not significantly affected by light-dark or CO2 treatment, indicating that dark treatment or CO2 exerted its effect by promoting the conversion of ACC to ethylene. This conclusion was supported by the observations that the rate of conversion of exogenously applied ACC to eth-ylene was similarly inhibited by light, and this inhibition was relieved in the presence of CO2. Similar results were obtained with tobacco leaf discs. The concentrations of CO2 giving half-maximal activity was about 0.06%, the ambient level of 0.03%. The modulation of ACC conversion to ethylene by CO2 or light in detached leaves of both rice and tobacco was rapid and fully reversible, indicating that CO2 regulates the activity, but not the synthesis, of the enzyme converting ACC to ethylene. Our results indicate that light inhibition of ethylene production in detached leaves is mediated through the internal level of CO2, which directly modulates the activity of the enzyme converting ACC to ethylene.

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spurr said:

EDIT:

I just fixed a typo, I first wrote that Rubisco activase is hindered when canopy temps exceed just over 92'F, but that's wrong. The correct temp is just above 89'F. So, make sure not to let canopy temp exceed 89'F

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thanks for the post. how big a role does temp play when trying to maximize the affect of supplemental co2? if 89f is the high end what's the low?

Damn spurr, great thread, thanks for the thorough reply.

all kinds of learnin' up in here

I just updated the previous post with easier to read screen shots.

forty said:

thanks for the post. how big a role does temp play when trying to maximize the affect of supplemental co2? if 89f is the high end what's the low?

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I wouldn't call 89'F the high end, I would call 86'F the high end, and that's at ~750 ppm CO2 with high irradiance (light intensity) of 1,500 umol/area^2/second. Dr. ElSholey (sp?) and a few others have researched cannabis in terms of effects from adding CO2, temp, and irradiance. Their research is lacking in terms of daily rates and effects, but the commonly found ideal temp range is ~82-86'F, and that's with CO2 supplementation and very bright light.

Another concern is the interaction between canopy temp and humidity (and leaf temp), in terms of how the air 'feels' to plants. This topic is called Vapor Pressure Deficit, and the higher the temp, the higher the RH must go to come close to sufficient (re ideal range) VPD of ~< 0.3 kPa. That is why I keep my day temp at ~78-80'F; that and it's easier to heat the room at night to 78-80'F during pre-flowering (re DIF). This grow I may use 80-82'F at canopy.

For healthy plants that are carrying out transpiration at a sufficient rate, leaf temp should be at least 1 or 2 degrees (F) cooler than surrounding canopy temp. I often see leaf temps a many degrees cooler than canopy temp. If leafs are the same temp as the canopy air, or warmer, there is a problem.

When looking at dataset graphs of rate of photosynthesis (Pn) increase as CO2, temp and irradiance increases, it's plain the increase in Pn from 80-82'F to 86'F is not huge. Another consideration is ADT (Average Daily Temperature), for best growth it's good to keep ADT > 75'F, at least > 70'F.

Other issues one needs to consider about heat is the effect of ammonicial nitrogen, namely ammonium (NH4). As the temp increases plants do less well using ammonium for N, and in turn photorespiration can increase, as well as other problems from hot temp and NH4 (roots and sugar).

I think keeping temp at leafs (canopy temp, measured in shade) from ~80-86'F is a good goal, with supplemental CO2 at ~900-1,100 ppm.

P.S. As temps increase so (most often) does ethylene production and release ...

CO2 has been on my mind quite a bit lately, thank you for posting all this up for my late-night reading

.

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

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....

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

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

kind regards from guineapig

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.

Another great thread...dude your a fucking asset!!!

Stay Safe