I see many repeated claims that plants absorb CO2 from the air.
CO2 goes into the stomata, while H2O evaporates and leaves those same stomata. The CO2 dissolves in the water in the plant sap, and then goes to wherever it's needed.
It occurred to me that in loose moist topsoil, there is a tremendous surface area for CO2 to leave air and get into the water. And that water does get absorbed by plant roots. Meanwhile there is plentiful O2 that soil bacteria can use to oxidize organic matter in the soil and convert it to CO2. In my imagination, this looks like a far more efficient way to collect CO2. Instead of wait for the CO2 from decaying organic matter to diffuse out of the soil into the air above and then enter stomata and dissolve in water there, cut out the diffusion step. The rising sap would carry CO2 to wherever it will be used.
It seems to me this would be easy to test. Grow plants in sealed containers with their stems sticking through small holes in an impervious barrier. Introduce CO2 containing C-14 either into the air above with the leaves, or into the air below with the soil the roots are in. Observe which way gets more CO2 incorporated into the plants.
Have experiments like this been done? My quick search did not find experiments like that. It found only the many-times-repeated claim that plants absorb CO2 through their stomata.
