104
CERTAIN TREE SPECIES
HAVE A SYMBIOSIS
WITH FUNGI
THE UBIQUITY OF MYCORRHIZAE
I
n 1885, a professor of plant
pathology at the Royal College
of Agriculture in Berlin named
Albert Frank was the first to see a
connection between fungi growing
on tree roots and the health of the
trees. Frank realized that these were
not pathological (disease-related)
infections but in fact underground
partnerships: far from suffering, the
trees seemed to benefit from better
nutrition. He invented a new term
for the partnership—“mycorrhiza,”
from the Greek mykes, meaning
fungus, and rhiza, meaning root.Mycorrhizae in action
False truffles are an example of
the fungal side of this partnership.
Nineteenth-century Prussian
botanists had found these fungi
under spruce trees, and noticed
that each tree root was drawn
toward a truffle, and wrapped in
a fungal husk. Although they did
not know it, the botanists were
witnessing a phenomenon that
is vital to many ecosystems.
Fungi are typically nourished
by a supply of organic matter, from
which they extract food by external
digestion. A deep layer of forest
litter is perfect. They pour digestive
chemicals onto their meal andabsorb the soluble organic
compounds produced through a
network of microscopic filaments—
hyphae—called a mycelium.
Plants rely on root hairs to
absorb water and minerals, such as
nitrates and phosphates. But there is
a limit to how far plant roots can
grow and therefore what quantity of
nutrients the root hairs can absorb.
The hyphae of mycorrhizae can
cover a much wider area, absorbingMycorrhizae on the root of a
soybean. In arbuscular mycorrhizae,
such as these, the tips of the hyphae
form clusters inside the plant’s root
cells, optimizing nutrient exchange.IN CONTEXT
KEY FIGURE
Albert Frank (1839 –1900)BEFORE
1840 German botanist
Theodor Hartig discovers
a network of filaments on the
roots of pine trees.1874 Hellmuth Bruchmann,
a German biologist, notes
the “Hartig net” is made of
fungal filaments.AFTER
1937 A.B. Hatch, an American
botanist, shows a beneficial
relationship between pine
trees and mycorrhizal fungus.1950 Swedish botanists Elias
Melin and Harald Nilsson
show that plant roots can
extract more nutrients from the
soil with the aid of mycorrhizae.1960 Another Swedish
botanist, Erik Björkman, shows
that plants pass carbon into
mycorrhizal fungi in exchange
for phosphate and nitrate.US_104-105_Ubiquity_of_mycorrhizae.indd 104 12/11/18 6:24 PM