Your question is rather ambiguous. Please explain more details. 

Fungi are among soil microorganisms. They predominate when the additions of fresh organic matter to the soil have high C/N ratio, as in forest soils. Anyway, thye are part of the bioagents that decompose plant residues to end in soil organic matter compounds. I don´t know the aim of your question, but, in general, fungi are actors in the chains of organic matter trnasformation in the soils, together with other microbs. Therefore, their sole presence doesn´t mean nothing; in order to be effective they need a substrate to decompose and, the amount of this substrate is normally the main factor in terms of soil structure develpment, that cause improved soil porosity and, eventually, better infiltration and less runoff.