How plants know where to root and Synthetic Soil

Two reasonably interesting, almost contradictory stories in the news today.

One comes out of a research center in Norwich, England. They've been studying how it is that plants know when and where to extend their roots.

The key, it turns out, is in a bunch of fuzzy hairs that are on the roots of the plant. These hairs act as sensory devices that explore the soil, much like we feel around in the dark. If they hit a wall, they slowly grope around until they find a way around it, or signal back to the plant that the way is blocked.

In nutrient-poor soils, some plants have adapted by growing longer hairs, which implies that breeding programs can be undertaken to grow the hairs in other plants, increasing their capability to intake nutrients.

http://www.telegraph.co.uk/earth/main.jhtml?view=DETAILS&grid=&xml=/earth/2008/02/28/sciroot128.xml

The other story comes out of Japan. A company called Suntory has invented what they call an 'urban soil' that is made out of synthetic urethane. 

Because it's lighter than soil, it's designed specifically for greening roofs and other urban areas that can't necessarily handle the weight of soil. The ultimate goal is green more of Japan's big city. In fact, Tokyo's government has passed a law saying that all buildings of a certain size *must* have gardens and trees planted on the roofs.

Still, given the research found above, I wonder how plants will know to root in the plastic soil...

http://www.physorg.com/news123148053.html

Perhaps the pseudo-soil is impregnated with rooting hormone? 

Actually, we get cuttings to root in perlite (although not synthetic, it certainly doesn't offer much for nutrients) regularly. People also commonly use little bits of foam to get plants to root. I suspect the actual formation of roots is dependent on hormone signals more than medium. However, those fuzzy hairs feeling around probably help to actually find what the plant needs.

I suspect Paul Stamets would have something to say about who is subtly guiding those hairs in one direction vs. the other as well. On his behalf I'll throw out my understanding (albeit limited) of endomycorrhizal fungi. These little mycelial threads actually grow into the root cells of the plant and form a symbiotic relationship. They can get needed nutrients (probably sugars) from the plant and the plant can essentially use the fungus as a root extender drawing nutrients from outside the range of its roots. As I've heard it, healthy forest ecosystems with all the complimentary mycorrhizal fungi will transport nutrients clear from one end of the forest to the other in order to balance deficiencies and maintain the health of the forest. In this way these mycelia essentially function as a "vitamin pill" for the forest. Thus healthy soil microorganisms make for a healthy forest ecosystem. Details in "Mycelium Running" by Paul Stamets.

Fascinating! Thanks for the insight, Dave!