Mycorrhiza tolerance for fertilizer levels

[don at bio-organics.com]

It has been well documented that excess levels of nutrients - luxury
levels - harm the mycorrhizal association with plants, in effect leaving
the plants dependent on just their own root systems.  However, we are
finding significant differences in opinion as to where the
excess-nutrient dividing line occurs, especially for phosphorus
amounts.  Does anyone know of good research on this topic, so that we
might better advise our mycorrhizae inoculum customers who wish to
convert to more biological growing methods?  Thanks in advance, Don
Chapman, Bio/Organics, Camarillo CA