What percentage of atmospheric CO2 is best for plants?

[Xist]

While we have discussed atmospheric CO2 levels in a ridiculously long thread immediately abandoned by its creator, somehow I did not realize that CO2 is measured by parts per million, not percentage.
I read elsewhere that too much carbon dioxide makes water acidic and plants may not create oxygen fast enough for their own needs. I also read that more CO2 will help plants grow, but without increasing other nutrients, they will be deficient.
This page states "Ambient levels of CO2 hover around 400-500 ppm. When you increase that level to around 1,000-1,500 ppm, you will see an increase in your yields and your plants will be much healthier." https://www.maximumyield.com/what-ar...ying-it/7/2610

Is this science fair material?

[oil pan 4]

They to do quite well with double the CO2 we have now.
More plant food, better growth right?
You can express atmospheric CO2 as percent, it would just be 0.04%. 400ppm sounds scarier.
Doesn't it sound more convincing that we are all going to die if plant food hits 400ppm instead of 0.04%?

I work around a dry ice machine where CO2 levels are 1,000 to 2,000ppm and I haven't died. The guy that works in that part of the plant is in it all day he isn't dead either. But I just fix it when he breaks it.

[redpoint5]

I haven't studied the subject, but there are universities that experiment with indoor farming, especially in Japan, and they often supplement their crops with additional CO2.

I wonder if merely increasing the air pressure (pressure chamber) would have the effect of promoting growth due to greater concentration of CO2?

[kafer65]

There is supposed to be a cherrie tomato plant in a mall in Japan that is as big as a tree from pressurized co2 to the roots

[jamesqf]

Originally Posted by oil pan 4

They to do quite well with double the CO2 we have now.
More plant food, better growth right?

CO2 is not plant food, sunlight is plant food. Put a plant in total darkness but plenty of CO2, and it will eventually die.

Also, more is not necessarily better. In addition to CO2 (and O2) from the air, plants generally need, water, sunlight, and soil nitrates, but too much of any of those can kill them.

[Xist]

Originally Posted by oil pan 4

They to do quite well with double the CO2 we have now.
More plant food, better growth right?
You can express atmospheric CO2 as percent, it would just be 0.04%. 400ppm sounds scarier.
Doesn't it sound more convincing that we are all going to die if plant food hits 400ppm instead of 0.04%?

I imagine that people do not pay attention to PPM. They might not even understand what it means unless you explain it (slowly). They just freak out about [seemingly] large numbers.

I read a comment that 6% CO2 is lethal. Since that would be 60,000 PPM, 133 times current atmospheric levels, hopefully people do not experience that naturally.

Originally Posted by redpoint5

I haven't studied the subject, but there are universities that experiment with indoor farming, especially in Japan, and they often supplement their crops with additional CO2.

I wonder if merely increasing the air pressure (pressure chamber) would have the effect of promoting growth due to greater concentration of CO2?

The results clearly showed that the rate of respiration decreased linearly with increasing total pressure at a high humidity.

https://www.ncbi.nlm.nih.gov/pubmed/23994480

Originally Posted by kafer65

There is supposed to be a cherrie tomato plant in a mall in Japan that is as big as a tree from pressurized co2 to the roots

When I copied and pasted this line into Google it did not show anything about a mall, but the rest seems relevant:

Dr. Kei Mori, a physicist from Keio University in Japan, worked with a Cherry Tomato plant that started in his basement. He gave light to the plant with a fiber optic cable which filtered out UV light, a process called ‘Himawari Sunlighting’. He also added pressurized CO2 in a gasket around the stem and root system. At some point, this plant was moved to a greenhouse which also simulated these conditions. Within 2 years, the tomato plant had reached 16 feet tall with 800 tomatoes. In 16 years, it was reported at 45 feet tall with 15,000 tomatoes. It was further reported that, under these conditions, the tomatoes would stay green until they were picked.

https://www.baraminology.net/preflood/tomato-mori/

There was a similar link to a document hosted by the University of Washington, but it only talked about filtered light, not increased CO2 levels.

[redpoint5]

Originally Posted by Xist

I read a comment that 6% CO2 is lethal. Since that would be 60,000 PPM, 133 times current atmospheric levels, hopefully people do not experience that naturally.

The concentration for death is less interesting to me than knowing the effects that doubling the concentration over the past 100 years has had.

Our respiration is controlled not by lack of oxygen, but instead concentration of CO2. If the air we breathe in already has a higher concentration of CO2 than what we are designed for, then it slightly alters our respiration impulse. What other things might be affected by a doubling of CO2 concentration?

Concerning the study you quoted, the full conclusion is that photosynthesis varies both positively or negatively depending on the pressure the plant is exposed to.

The rate of respiration decreased linearly with increasing total pressure up to 0.2 MPa, and increased with increasing total pressure from 0.3 to 0.5 MPa at a low humidity. The rate of net photosynthesis decreased linearly with increasing total pressure under a constant partial pressure of CO2 at 40 Pa. On the other hand, the rate of net photosynthesis was clearly increased by up to 1.6-fold with increasing total pressure and partial pressure of CO2.

[oil pan 4]

I don't even worry about CO2 exposure till it hits 3,000ppm.

If CO2 isn't plant food neither is sunlight.
Sun light is more harmful to humans than CO2.

[RedDevil]

Yeah. Well if it were that simple.

https://www.independent.co.uk/news/s...-a8342521.html

Basically there are 2 types of plants: those who move CO₂ actively towards an enzyme (RuBisCO) that absorbs it to prevent it from erroneously taking on oxygen and wasting energy, the so-called C4 plants; and plants that do not (C3 plants).

It was thought the C3 plants would benefit from having higher levels of CO₂, but in the long run they don't!

Most models of how plant growth and crop yields will be affected by the CO₂ released by burning fossil fuels have assumed that regular C3 plants may perform better. Meanwhile, the RuBisCO in C4 plants already gets enough CO₂ and so increases should have little effect on them. This has been supported by previous short-term studies.

The new Science paper reports data from a project that has been comparing C3 and C4 plants for the past 20 years. Their findings are surprising. As was expected, for the first ten years, C3 grasses grown under extra CO₂ did better – but their C4 equivalents did not.

However, in the second decade of the experiment the situation reversed, with the C3 plants producing less biomass under higher levels of CO₂ and the C4 plants producing more.

It seems that this perplexing result may be because as time went by, less nitrogen was available to fertilise growth of plants in the C3 plots and more in the C4 plots. So the effect was not just due to the plants themselves but also to their interactions with the chemistry of the soil and its microbes.

So there you have it. It is bad, even for many plants that were expected to benefit due to their C type.

Food crops will thrive, if carefully fertilized.
Natural areas will change.
Over time, bacteria may evolve to bind more nitrogen to compensate. But then phosphorus may run out, key minerals, whatever.
Life, even wildlife, will be sustainable only if properly monitored and supported.

The good news is: we can feed the growing world population; there will be more food available in the future.
The bad news: It is going to take a lot of work...

[Xist]

I have only slept four hours a night for the last few nights. RedDevil, does that say that CO2 benefits plants as long as they have enough other nutrients?

As for the full conclusion that RedPoint shared:

High total pressure bad at high humidity.
Total pressure up to 0.2 MPa bad with low humidity.
Total pressure 0.3 to 0.5 MPa good with low humidity.
Increasing total pressure under constant partial pressure of CO2 at 40 Pennsylvania bad.
Increasing total pressure and partial pressure of Colorado2 good.

So, total pressure 0.3 to 0.5 MPa with low humidity and increasing total pressure and partial pressure of CO2 are good. The other modifications are bad.

Is this correct?