Hey Benedict, welcome to permies
Perhaps I’m misunderstanding your question, but you’re wanting to know more about plant nutrition?
The Wikipedia article on the subject is decent, and references a number of scholarly articles that may have what you’re looking for.
http://en.wikipedia.org/wiki/Plant_nutrition
Is there proof, and is it true? Well, it depends - remember that we as people often make the mistake of assuming that what is already known, is all there is to know. As far as we can tell plants are taking up minerals/nutrients and using them, and exuding
carbon, among other things, into their surroundings.
Are their mistakes in our current knowledge? Probably. Are there large gaps in our current knowledge? Absolutely.