This is the forward to a paper published in 1998:
Forty years ago, Erik Bjorkman injected labeled glucose into the phloem of three Norway spruce trees and measured its transfer to nearby individuals of the achlorophyllous plant, Monotropa hypopitys[1]. Many similar experiments have since been done with various plant combinations (although all with chlorophyll since Bjorkman), using isotopes of carbon, phosphorus, nitrogen and calcium[2–7]. With a single exception, isotopes have been found to move from one plant to another as long as the plant species in question share mycorrhizal fungi. This finding supports Bjorkman’s original hypothesis that movement is predominantly via mycorrhizal hyphae. In the one exception, 32P applied to mycorrhizal hyphae was distributed amongst tree seedlings linked to the hyphal network (two pine species), but when applied to the seedlings did not move into the network, suggesting movement along gradients of relatively high to relatively low concentration[8]
A moveable feast: the evolution of resource sharing in plant–fungus communities Perry, David A Trends in Ecology & Evolution, Volume 13, Issue 11, 432 - 434
Apparently there’s decades of research corroborating the idea.
…what change did Occupy effect?