Your bonsai may be on shrooms--and thats good

Mycorrhiza - the friendly fungus

Not all fungus is bad for your bonsai. Mycorrhiza fungi can form a symbiotic relationship with your bonsai's root system.

Bonsai store excess sugars from photosynthesis in their roots. The mycorrhiza attach to the roots to absorb these sugars, but in return the plant gains the use of the fungi to uptake nutrients from the soil. This is more efficient than if they were to use their roots alone. This is partially because the fungus is so fine that it can get to parts of the soil the roots otherwise couldn't.

It is believed they are especially beneficial to the host (bonsai) in drought conditions and poor soils.

If you repot your bonsai and notice a thin white film between its roots it could be mycorrhiza.