Mulch plants for different nutrients

I'm looking for deep-rooted mulch plants to bring up magnesium specifically, but im working on a larger list of other deep-rooted mulch plants too, and what nutrients they're rich in.

Zone 5/6 MI, clay soil, ample water, low elevation, sun areas and shade areas.

I've got comfrey and mullein already but I don't know what nutrients they're highest in

Here's a database of plant chemical constituents: https://phytochem.nal.usda.gov/phytochem/chemicals/show/11854?et=