Plants photosnythesize better with an abundance of CO2. Animals thrive with abundant levels of oxygen. The time periods in earth’s history when we had the largest plants, the largest animals, and the highest concentrations of CO2 and oxygen all coincide. It is intersting to imagine how the world might have been different then. It was certainly was very different than our world today, and as the levels of these gasses change in our atmosphere, we should expect plants to grow differently over time.

From the Regenerative Agriculture Podcast with Jerry Hatfield:

John: Jerry, when you spoke about growing in grow chambers, you mentioned that you saw an increase in oxygen content, as well as CO₂. This is something worth elaborating on, because I’ve observed the same thing in the field when we have plants that are photosynthesizing well.

Many people have this idea that there is a conflict between CO₂ concentrations and oxygen concentrations. And I don’t see it that way at all. When we have higher CO₂—specifically when we have higher CO₂ being released from the soil—and when we have good photosynthesis, we get higher oxygen content in the air.

Jerry: That’s correct. And that’s counter to our thought process. You only see that when you start measuring both things simultaneously. I’ve been looking at the literature on the number of papers that actually measure oxygen content within the soil—even the CO₂ content within the soil. It’s really pretty sparse.

It’s not a trade-off between oxygen and CO₂. A good biological system generates more CO₂ because the soil has more pores and more structure to allow gas exchange to occur. That keeps our oxygen content high, which then promotes more biological activity, which generates more CO₂.