If I told you there was a large mass of fungus infecting the roots of that lovely pine tree which shades your front lawn, would you be worried? Would you buy a strong fungicide if I said that this fungus survived by sucking valuable sugars, vitamins, and other nutrients out of your tree's roots?

Many trees and plants not only host mycorrhizal fungi–they have actually come to depend on them. As the fungi grow, they send fine tentacles streaming into the soil. These tentacles help channel large amounts of water and nutrients back to the host tree, far more water than the tree would be able to trap with its roots alone.

One study found that conifers with the fungus are twice as likely to survive a drought as those without. Some mycorrhizal fungi help their host tree in other ways too, secreting a tree hormone that causes the roots to grow new root tips, and a hormone that increases the longevity of these new roots.

Other fungi release natural antibiotics into the soil, further protecting the tree. In fact, the seedlings of many tree species will die if fungus does not develop around their roots during their first year of growth.