Living trees fix carbon in their trunks / branches but this is released back into the atmosphere when the tree dies and falls over.

Photosynthetic capacity (A) is a measure of the maximum rate at which leaves are able to fix carbon during photosynthesis.

Most of the well-recognized phototrophs are autotrophs, also known as photoautotrophs, and can fix carbon.

However it can fix carbon in reactions like:

Plants, algae, and many species of bacteria (cyanobacteria) fix carbon and create their own food by photosynthesis.

C3 plants use the Calvin cycle to fix carbon.

For example, soils with depleted biological diversity are much less able to fix carbon, accentuating the effects of climate change even further.

Organisms that grow by fixing carbon are called autotrophs-plants for example.

They contain the pigment chlorophyll, and use the Calvin cycle to fix carbon autotrophically.

Plants take up C by fixing atmospheric carbon through photosynthesis.