A number of desert species are nitrogen fixing, obviously in conjunction with mycorrhiza. I have specifically seen recommendations to plant Bursera (as a bonsai!) using mycorrhizal innoculation.

I know that each legume species forms relationships with a specific fungal species but that they also often work with closely related species. Non-specific mycorrhizal innoculations are likely to be a general blend of arbuscular mycorrhizae which may or may not be effective for the plants you are trying to grow.

Right. Thanks. From what I've been able to glean online, it doesn't sound like it would hurt to try. Wondering now if there's any sense in watering the stuff in on my established burserae (all re-potted this winter). From what I've read, proper procedure is to dust the roots when re-potting, so I don't know if watering in would do anything.