Hi Jerel, check out recent research by Dr James White on the rhizophagy cycle: https://www.youtube.com/watch?v=yMr3_tGeAu8

He has shown that plants can directly ingest microbes through the root tip and strip off the cell wall for use as a nutrient source. It’s not clear (to me at least) whether carbon is also used by the plant during this process, but it seems reasonable that it would be. Maybe @john.kempf can add some thoughts. Nitrogen tracer studies have shown that plants can directly take up organic N, but here again I don’t know if that research looked at what happens to the C attached to the N during this process. I could dig up some papers if you would like to read further.