Photosynthesis and O2 release vs. Respiration

[Kampi]

I've got a Guru question: In an aquarium is the amount of CO2 being captured by the plants during the day, being released back into the water when the lights go out at night (a ratio of 1:1)? Is this the same, in reverse true for O2; released into the water during the day and used by plants at night?

I think this is stoichiometry, but it has been awhile. There are assumptions like, day length is equal to night, CO2 availability and estimative index for nutrients are perfect. Are there other considerations?

 

[rockhoe14er]

I'm not a guru but if plants absorbed as much o2 as they produced during the day at night then no animals would be alive on the earth. This is the same with co2. I'm not sure what the ratio is but i know it's not 1:1. I think it's difficult to establish a ratio because size of the plant comes into play as well as the type of plant. Some plants consume much more co2 than others and vice versa.

 

[scottward]

No.

Remember that Carbon is the "building block" of life. The plant is going to take the carbon out of the CO2 and use it to, well, grow! Therefore it's going to take in a lot more than it puts out.

 

[Tom Barr]

I've got a Guru question: In an aquarium is the amount of CO2 being captured by the plants during the day, being released back into the water when the lights go out at night (a ratio of 1:1)? Is this the same, in reverse true for O2; released into the water during the day and used by plants at night?

I think this is stoichiometry, but it has been awhile. There are assumptions like, day length is equal to night, CO2 availability and estimative index for nutrients are perfect. Are there other considerations?

There's an issue, units that are scaled appropriately.
Say per gram of biomass of a species and then the rates of growth.
More growth, more O2 produced and more CO2 demand.

And it is also important to realize that the CO2 is not the source of the O2 produced by plants, those are not coupled. The source is from H2O in the light rxs and the electrons are used for reducing NADP into NADPH and the extra H+'s are used to make ATP from ADP.

CO2 is reduced later in the Calvin cycle.

When plants use the reduced carbon for energy later, they release CO2, but a lot gets resorbed by aquatic plants also during the day depending on the CO2 demand in the plant. During the night, most of the CO2 is released.

I think it would be tough to put a figure on it and generalize, since there is such a strong dependency on rates of growth, and the biomass amount variables, and species variables. After all, everyone has different biomass % and also different plant species which also have different rates of growth naturally/intrinsically/metabolically.

We also have variables like surface turnover, and gas transfer form the filtration etc, or Fick's 1st law of diffusion to add to this model as well.

It gets pretty messy really quick.

You can make a simple drawing and put arrows where the O2 comes in and goes and for CO2 as well.

You'll find it gets complicated quick.

Regards,
Tom Barr

 

[Biollante]

Complexities Abound, yet Even the Complex May Be Basic…

Hi,

Not to detract from the complexities Tom Barr describes…

It is fair to agree with rockhoe14er and generalize based on the conditions put forth in post #1 that assuming healthy plants carrying on photosynthetic activity, increasing plant mass that more oxygen is produced than consumed.

Any number of high school texts will describe simple demonstrations of this phenomenon.

Biollante