CO2 Question

[Daithy]

I see that the "day" temperature needs to be higher than normal, 23–25 centigrade, when using added CO2 they say around 30.

I was just wondering. Wouldn't high temps be counter productive? Stomata need to open to let in CO2, when that happens water is being lost/released. If we raise the temps, stomata will tend to close to conserve water, no? Unless the 30 is a real sweetspot.


Does anyone have an empirical explanation as to why you need higher temps to utilise CO2 account for the loss of water?


Thanks.

 

[GrowinDad]

I think you have it backwards and only need to suppement CO2 if running high heat. It helps deal with it, but you wouldn't want to raise hte heat so you can use CO2.

 

[Dr. Who]

Hmmm......You most certainly do have to. To make the rise in Co2 effective !!!

At 70F the effective amount of usable Co2 ppm is 800.
At 85F the effective amount of usable Co2 ppm is 1300.

"Co2 UPTAKE WITH NO LIMITING FACTORS: As the intensity of the light increases, the plant requires higher temperature and higher concentration of Co2." From Ed Rosenthal's book Marijuana growers handbook.

From darkness. The rate of photosynthesis has the greatest increase as the Co2 level climbs from 0 - 200ppm. Under low light conditions (150mols or 1150fc [12,330lux]), the rate of photosynthesis increases as Co2 levels rise to 400ppm. Increasing the Co2 concentration beyond that without increasing the light intensity does not result in a higher rate of photosynthesis. The plant cannot take advantage of higher Co2 levels until the light intensity increases.

At a light intensity of 600mol (4600fc / 49,310lux) the photosynthesis increases more as Co2 concentrations are increased to that 400ppm. The rate of increase declines a bit after that, but the photosynthesis rate continues to climb as Co2 levels reach 600ppm. Above 600ppm, the photosynthesis rate continues to climb but at an even slower rate, until the rate levels of at about 1200ppm.

By increasing light intensity, you encourage you plants to absorb even more Co2 which increases growth and yield. When the plants receive between 4500 - 5500fc (48,240lux) of light, they can utilize between 1200 - 1300ppm of Co2. While very few gardens are supplied with more then 7500fc (80,400lux) of light, at that intensity the plants can utilize up to 1500ppm of Co2.

Increasing the ppm levels above 1500 is a waste of Co2 and thus money, in so much as the plant has hit the wall so to speak (the photosynthesis increases over 1500ppm Co2, even with an increase in light intensity is at a rate that makes the use versus cost ratio ineffective) on the available lighting intensity versus effective utilization of available Co2!

Now read this paper to confirm the temp increase needs...
http://www.rsc.org/learn-chemistry/content/filerepository/CMP/00/001/068/Rate of photosynthesis limiting factors.pdf


See what I mean?

Doc

 

[Dr. Who]

I see that the "day" temperature needs to be higher than normal, 23–25 centigrade, when using added CO2 they say around 30.

I was just wondering. Wouldn't high temps be counter productive? Stomata need to open to let in CO2, when that happens water is being lost/released. If we raise the temps, stomata will tend to close to conserve water, no? Unless the 30 is a real sweetspot.


Does anyone have an empirical explanation as to why you need higher temps to utilise CO2 account for the loss of water?


Thanks.

I think you have it backwards and only need to suppement CO2 if running high heat. It helps deal with it, but you wouldn't want to raise hte heat so you can use CO2.

@chuck estevez

See the answer above.

 

[Daithy]

Great reply, Dr. Who. However, your article does not address temperature in correlation with higher CO2 uptake. Yes, the more light, the more CO2 is utilised, because more photosynthesis can occur due to increased light, but what has it got to do with higher than optimum temperature?

"Light dependent reactions use light energy and so are not affected by changes in temperature."

"Although the light dependent reactions of photosynthesis are not affected by changes in temperature, the light independent reactions of photosynthesis are dependent on temperature. They are reactions catalysed by enzymes. As the enzymes approach their optimum temperatures the overall rate increases. It approximately doubles for every 10 °C increase in temperature. Above the optimum temperature the rate begins to decrease, as enzymes are denatured, until it stops." -- Just to add Enzymes in plants have optimum temperature around 25 degrees centigrade, over 30 is beginning to be quite hot

"If carbon dioxide and light levels are high, but temperature is low, increasing temperature will have the greatest effect on reaching a higher rate of photosynthesis." --- This is not very specific, what is "low"? Increasing how much? And how exactly does it help?



Thanks!