Fungi Fixing Nitrogen for plants

Its not just legume or adler that can fix nitrogen form the air.
Fungi can also do it too and they exchange it with plant room for sugar.

https://en.wikipedia.org/wiki/Suillus_tomentosus#Habitat

This is from your reference S Bengi;

Suillus tomentosus forms tuberculate ectomycorrhizae (mycorrhizae that are nodular) with lodgepole pine (Pinus contorta var. latifolia). Recent work has shown that acetylene is reduced by the nodules which means that nitrogen is being fixed by bacteria within the nodules.[11][12] This system is functionally similar to the root nodules in legumes like clover. Lodgepole pine can be found growing on gravel pits or other extremely nitrogen deficient soils. Lodgepole pine with its S. tomentosus symbiont is one of the most common pioneer species in northern forests. It colonizes highly disturbed soils and creates an environment suitable for other species to colonize.  

Just like Legumes this fungi doesn't actually fix nitrogen it harbors the bacteria that fix nitrogen. Suillus tomentosus is one of the extomycorrhizae and it is specific to conifers, which is why the reference to the lodgepole pine is made (lodge pole pine got its name from the fact that it was widely used for Tipi poles).

Do you know if there are similar fungi that "help" fruit/nut trees with their nitrogen need by hosting nitrogren fixing bacteria?

Bill Mollison mentions 200lbs/acre can be fixated by fungus in a mature conifer forest. According to Noss, redwood forests, the fastest growing terrestrial ecosystems on earth, are ultimately limited by available nitrogen. I do not recall him mentioning a number for fungal nitrogen fixation though.

Yes S Bengi there are several types of mycorrhizae that work with fruit and nut trees, both ecto and endo are needed for a complete supporting symbiotic system.
There are many species of both that work well in this manner and the research is ongoing so for now it would be guess work to suggest a best fit.
Not to worry though most of the Mycologist that are selling mycorrhizae, sell both in a single package and they include most of the known species so you have the best chance of getting that perfect fit for any fruit or nut tree.

The trick it seems is to make sure you are getting them from someone that 1. is a mycologist doing business in mushroom spawns (there are several out there) 2. offers a mycorrhizae package designed for either overall use or hardwood trees.