Comment by throwup238

Depends on the ecosystem. Anything embedded into bogs or peatland like roots will generally not decay at all, instead building up a very thick layer of captured carbon as peat.

Plants get most of their carbon from CO2 anyway, so in most cases carbon accumulates in the loam (outside of intensive agriculture at least). They produce far more than decomposers have a use for and that's how CO2 accumulates in soil. It only needs to be replenished by the rest of the carbon cycle because of erosion.