I am interested in their presence in submerged plants, not in emerged ones. Have you observed this kind of symbiosis in your aquarium tank? Can you give me some information about the plant/s species involved and their success?
Does it grow on emersed and submerged plants too? I have heard about it growing on terrestrial plants before, like the obligate mycorrhizal plants and non-obligate. It is a quite interesting symbiosis.
Yes, they exist in natural habitats in both types of plants (emerged and submerged) and are quite important for isoetid species (eg. Isoetes spp.). It can be a crucial help to obtain phosphorous from substract but I ignore the relative gain for a planted aquarium stability with our constant intervention in nutrient supply.
Mycorrhizae aren't nearly as important in out nutrient supplimented aquariums as they are in the wild. Also, mycorrhizae are habitat specific, meaning that fungi from your local soil very likely aren't going to be suitable for your plants and vice versa. All in all, they don't play a role in our aquariums. Native biotope soil based aquariums are the exception, and there mycorrhizae can play a major part in the overall ecology of the aquarium.
A long time ago I saw what must have been mycorrhizae on, of all things, Ceratophyllum, which does not have roots. I grew some in a gallon jar with soil on the bottom, and, later, when I removed the plant, gobs of mud clung to the stem where it had been pressed into the surface. I washed away the mud and found a dense mat of colorless half inch hair-like threads coming from the stem and even from the leaves. Under the microscope these threads looked like fungal hyphae. I could clearly see the cross walls separating the cells.
I think it would be slighty difficult to assess the benefits to a species which grow normally very fast, but could you infer anything relating to more resistance to bad conditions (not optimal levels of nutrients)?
do you know something about the ecology of the fungus species? are they specially aquatic species? do you have some idea about the success of planting terrestrial mycorrhizae in aquariums?