Because if from PoxC we can appreciate the health of the soil, does this integrate or not the presence and the specific richness of arbuscular mycorrhizal fungi (AMF) in soil?
An interesting question . I doubt , PoxC can anyhow predict the abundance of AM fungi in soil. No doubt , abundance of AM fungi in soil adds carbon through glycoproteins , a more recalcitrant form of carbon .
Better you go for autoclaved citrate extractable protein that can give an idea on glomalin. As you must know that glomalin (glycoprotein) is produced by Arbascular mycorrhizal fungi. Glomalin is the primary indicator of AM fungi. But permanganate oxidizable carbon that is active carbon I don't think can predict AM fungi population.
The production of the glomalin glycoprotein is refractory in soil. For every 2 parts of glycoprotein an addition part of soil organic carbon is found in the soil. The amount of oxidizable organic carbon increases with the increase in overall soil carbon and AMF mycorrizal proteint. As the soil carbon increases the oxidaized soil organic matter the glomalin the quantity and diversity of mycorrizae will increase.
This responses need to tested under your condition but that would be my expectation from my sexperience and the literature I have reviewed.
Suggest confirming by both your own studies and the survey of the literature.