Suzanne Simard has a bunch of chemical analysis that says yes, and most of her testing was in the PNW and western Canada (BC and... Alberta?)

A lot of the other literature on the complex relationship of soils and trees (and trees and trees via soil life) were instigated by her observations.

She was trying to get NW foresters to stop bathing everything in herbicides before replanting clearcuts. They always struggled more than anticipated.