Maybe a better way to put this question is:
Given an isolated garden bed, that had no external inputs except light, water and air. If you were to grow plants in it, compost those plants and add them back to the garden. Over time (with no external inputs) would you end up with more nutrients over time or less?
To add context, I have a yard with soil, a few trees, lots of grass and a couple garden beds. I rake the leaves, cut the grass and compost them. Do the trees and grass only take nutrients from the soil, or do they create new nutrients that I can compost and add to garden. Meaning over time my yard as an enclosed system, does it lose or gain nutrients; assuming I also recycle all fruit and vegetable back through the compost.