Well, the fact that now people have decided to put a house (or building) between plants and the Earth's crust (which I am completely in favor of) doesn't change the need of those plants to have an established food web. So if you want your plants to do well, wherever you have them, you need fungi. Not including such an essential organism means that you will have to supply to the plant what the fungi would, which is not cheap and you will have nutrient/fertilizer runoff. Is just so much simpler to have a good little buddy connected to the plant nurturing the roots, not to mention that the fungal mycelium will aid on the substrate retention, win win if you ask me.
There is much to be learned about these new artificial habitats, but I believe that future green roof research should include mycology and microbiology. I hear there is a pioneer mycologist out there (didn't catch the name) that is starting to look into this. That researcher should not be the exception, that person should be the norm. Let's have teams of people working together looking at the health of the ecosystem, one hydrologist looking at water retention, one plant scientist working with plant health and selection, one mycologist working with symbionts and pathogens, one architect looking at the design to optimize space. I bet that considering the perspectives of varied fields of study will improve drastically the quality of research, our understanding of the environment, and the overall efficiency of the product.
And by the way, whomever is reading this, I am a mycologist, I am interdisciplinary, and I need a job.
:)