system
Given the following post, respond as if you're commenting on Reddit:
human
Are forests and jungles growing more rapidly now that there is an increase of CO2 in the air?
gpt
In photosynthesis there are 3 metabolic pathways for carbon fixation from CO2. In forests and jungles we are concerned with the C3 and C4 pathway (the CAM pathway is only found in arid plants). These pathways impact how a plant responds to elevated CO2 levels.

In the C3 path oxygen competes with CO2 in the presence of the first enzyme, RuBisCO. Meaning that the enzyme can't distinguish between oxygen and CO2.  Incorporating oxygen ultimately results in a toxic compound later on that must be disposed of through photorespiration which uses energy. So the ratio of the gases in contact with RuBisCO matters. More CO2  successfully being bound means less energy lost to photorespirstion.  Increased CO2 can benefit these plants. 85% of plants use this C3 pathway including rice, wheat and trees.

The C4 pathway evolved next and it removes the energy lost to photorespirstion by only allowing RuBisCO to bind CO2. This is accomplished by putting the enzyme in a newly evolved chamber and selectively exposing it to only CO2. These plants are pretty much already maxed out at what they can handle at current CO2 levels. They don't get any benefit from rising CO2 levels. These include plants like corn and grasses.

Forests and jungles contain both C3 and C4 plants. C3 plants have the capability to grow more in the rising levels but climate change also bring along big temperature and rainfall shifts which can negatively impact the health of the C3 and C4 plants alike.