Recalcitrant carbon is inorganic carbon which has a crystalline structure that is excellent for trapping life giving minerals/metals and as a soil structure that acts like a microbe “hotel”. My take, more or less, is that it is useful because Biochar has a tremendous amount of external AND internal surface area. This is perfect for the Amazon because with the amount of rainfall/flooding they get, you need shelter for minerals and microbes so they are not leached from the soil. Recalcitrant carbon sequesters 25-50% of the carbon from its source feed stock for 1000 years. This is interesting from a purely sequestration point of view if you have created a problem for yourself by dumping too much CO2 into the air that you need to fix. Recalcitrant carbon stays in the soil so long because it is inorganic and not bioavailable to fungi/microbes/plants. Now things got interesting. Labile carbon is the active/bioavailable type that may be in the form of a solid, liquid or a gas. Labile carbon from bioremediation sequesters less than 10-20% for 5-10 years. This carbon is the stuff life is made from and the existence of or lack of determines the fertility of the soil and therefore the bio diversity of the life in the soil.