A single plant does produce oxygen while it's alive, and the carbon is bound in its growing body.
But that carbon is all released back as it decomposes after its death.
On a "whole forest/whole year" perspective, there is normally an equal mass of plants growing and being decomposed, and thus the net oxygen effect is zero.
> But that carbon is all released back as it decomposes after its death.
> On a "whole forest/whole year" perspective, there is normally an equal mass of plants growing and being decomposed, and thus the net oxygen effect is zero.
Sure, if you're talking about a timespan of one hour, one month, one year, etc then it's definitely possible for biological processes in a forest to expel carbon in the form of CO2 in equal volumes that were sequestered by plants. You could even have an overpopulation of some kind of insect or fungus cause a forest to temporarily become a net contributor of atmospheric carbon.
But over the lifetime over the forest, the net effect is obviously massive CO2 sequestration and massive O2 production. If the net carbon impact was zero over the lifetime of a forest, then forests would have no soil. But we know that not to be the case. Forests grow, they accumulate soil, etc.
Despite constant heavy rains and erosion, soil in the Amazon rainforest is often several meters deep and spans an area of over 2 million square miles. That's a lot of carbon sequestration!
> I assume it reaches an equilibrium after some time
Yep definitely and in part because CO2 only makes up ~0.04% of our atmosphere. Photosynthesis processes slow when CO2 levels fall and increase when CO2 levels rise. But as well as know atmospheric CO2 levels are rapidly on the rise and is outstripping the ability of large forests to sequester it.
But that carbon is all released back as it decomposes after its death.
On a "whole forest/whole year" perspective, there is normally an equal mass of plants growing and being decomposed, and thus the net oxygen effect is zero.