Who was the guest lecturer?

"they use the plant for Carbon, and contribute other nutrients to the plant"
     What they really use the plant for is energy, and Hydrogen bonded to Carbon stores the energy!
-Phosphate critical for living cells. ATP
     This is so they can store energy!  Follow the energy!
-Mychorrizal associations contribute 20-80% of P needs.
     They need energy, and plants need P for ATP to store energy.   
-Plants w/o mychorrizal association explore 1-2 cm3 of soil around roots.
-Plants w/ myc ass. explore 12-15 cm3 of soil around roots. 
     Interesting research.  That might be on the conservative side.
-When P or N is limiting, plants support mychorrizal assocation. 
-High concentration of P or N in plants create more demand for Carbon. Then plants reduce C contribution to mychorriza or eliminate association. 
     No one buys something if they can get it for free.  Plants aren't going to give away energy if they don't need to!
-Plants spend less energy in the mycorrizal association than producing root mass for nutrient uptake.
     If they didn't, there would be no interaction.  Nature is very energy efficent... i.e. lazy 
-Hyphae (structure) reach up to 10 cm from roots.
     Impossible!  Just kidding.  very interesting.
-Phosphorus is largest nutrient uptake by myc fungi to host.
     very interesting
-Other nutrients taken up N, K, Mg, Ca, Mn, Zn, Cu
     Through Mychorriza as well I assume? 
-Increase plant tolerance to water stress. Hyphae extract water from small pores. 
     I have heard fungus can break down Organic residue using 10x less water than if Bacteria does as well.
-Supress root disease, improve plant health, mechanical resistance.
-Produce Glomalin to bind soil particles.
     Good stuff that glomalin!
-Excess fertilizer leads to less myc association. 45 lb/A/Yr reduced colonization by 50% 
     This goes along with the two bullets above
-Negative correlation to high P 
     again, if the plants can get what they need using less energy than by trading with the mychrorriza, then they will use the energy themself or store the excess energy in the seed.  High available P in the soil saves the plant energy.  (might not feed the soil as well though?)
-Plants depend on myc to different level. Flax 90%, Corn 80%, Sorghum 60%, Wheat 30%.
-Brassica are non-host of myc fungi
     good to know.

Good post. 
      There have been some posts on Agtalk where N was sidressed on 60" centers and pictures showed that corn produced more roots on the sidedressed side of the plant.   The (incorrect) conclusion was that fertilizer made the roots grow rather than that the plants got lazy and only grew roots there and stopped producing roots and trading w/ fungi everywhere else.   95% of the corn I have grown has been with no N applied and has been very profitable.  I agree with what Gabe Brown says.  He isn't selling anything BTW.

No cell construction can take place without energy.  It is the most coveted currency in the cosmos.  Earth is not inhabited by humans, animals, insects, plants, and fungi.  It is inhabited by cells and they multiply by division, organize, and control you.  Hows that for AH HA? Follow the energy!