Hello everyonel!

The association of organic substances (OM) with mineral surfaces is one of the major stabilization processes of SOM in soil. Depending on the soil mineral reactivity, solution properties (e.g. pH, ionic strength) and character of organic compounds (e.g. microbial or plant derived compounds), this sorption will be more or less reversible as it is proposed to occur in different zones (onion layer) with different binding strength and mechanisms (e.g. ligand exchange, electrostatic, ...).

The question:

It is often stated in literature, that the organic matter, which is associated with minerals (MAOM), is “protected” against microbial decomposition. Which process does “protected” precisely refer to?

I understand that diffusion rates of OM will decrease and OM can e.g. be adsorbed between layers of clay minerals limiting microbial access to the SOM. However, enzymatic depolymerization with subsequent diffusion of the compounds to the microbial decomposers should still be possible (?) and was revealed by studies.

What do I miss? Can anyone please enlighten me how mineral association “protects” SOM? Which processes are important , beside diffusion and intercalation? Maybe some recommendations of literature?

Thanks a lot!