A long time. Depends on the temp. warm soil temp. helps break down faster. It last as long as there's product left for the microbes to eat. I would have to say that a high cec would break it down faster as well. UF is the fastest way to make good top soil in the world!! What do you think of that. I can't remember all that stuff about the expensive ferts but that's about as good of answer as I can think of for now.
Now I read back to see If I had answered properly and I noticed you said "mechanism" I can't remember the slide shows that well but I think it has something to do with sugars and conversions?