Mycorrhizae and root hairs are abundant and active in winter. Our tree
concept must be expanded to include these facts.
By Dr. Alex L. Shigo
With repeated observation of
any part or process of a system, facts emerge that must be included in the
concept of that system. Consider the cell theory, germ theory, DNA,
antibiotics, and even the branch collar. In all cases, new facts made it
necessary to expand our concepts for these systems.
Almost all of the studies on trees have been done on
seedlings, or on aboveground parts in summer. Few studies have been done
on mature trees outside. Deadwood anatomy has been and still is confused
with living tree anatomy. An understanding of anatomy must precede any
understanding of physiology.
Even fewer studies have been done on below ground parts of
trees in winter in temperate climates.
This article discusses results of
observations on belowground parts of trees in winter from 1992 to present, in
New Hampshire, United States. Some philosophy is given as a plea for Modem
Arboriculture. An expanded concept of a tree is given. Trees are
viewed as opportunistic multiple systems. Abiotic and biotic factors are
discussed as initiators of processes.
Trees have five major phenological stages: Start,
leaves, growth, storing and rest.
Reproduction is a sub-pattern that usually starts near stage
two. It is impossible to generalize these patterns because there are
almost as many variations as there are species. However, every tree system
must start again from a quiet period. Every tree must produce new leaves
or needles for photosynthesis. Every tree must increase in mass; this is
growth. Every tree must store ingredients essential for survival.
Every system must rest. Most trees also have reproductive cycles.
Some are extremely complex in their patterns.
Dormancy is usually thought of as a period of rest where
processes essential for life function at a minimal rate. Dormancy does not
mean stopping! Stopping is death.
The second law of thermodynamics states that no system will
survive unless it receives a continuous supply of energy to maintain order.
In order to survive, trees must also have a supply of water and elements.
These points must be remembered as the discussions go on.
Trees as business conglomerates
Trees are often referred to as living systems. Many of the problems
with understanding phenological stages could be clarified if a tree was viewed
not as a single system, but rather as a cluster of systems connected in highly
ordered ways. Maybe a tree is more like a business conglomerate. If
the business conglomerate analogy could be accepted, then many different parts
of a tree could be in different phenological stages at the same time. Many
aboveground stages are different from those belowground. In the sense of
natural dualities, the business conglomerate analogy is a better way to view a
If a tree is a cluster of systems, and all systems
require a continuous supply of energy to maintain order, then it appears that
the different systems would require energy that came from storage. It is
difficult to accept that energy from photosynthesis could supply all systems at
the same time. Some timing or allocations for timing must be there, and
also, a supply of energy in a stored state.
This we know is true because trees first form ATP, which is used to form glucose
which then forms cellulose, starch and a great number of other substances.
Still, glucose is the fuel that makes it possible for the tree to survive.
Trees do have ways of storing energy reserves and for regulating the use of the
energy for processes to survive.
Water is another essential for life. We think of water,
mostly, in its liquid form. Water molecules enzymatically removed or
inserted are essential for many processes and products, from cellulose to starch
and back to glucose. Trees store water as bound water on the hydroxyls on
cellulose. The water is bonded to the cellulose by very weak, but
significant, hydrogen bonds. When any force greater than hydrogen bonds is
exerted, the bound water then moves to liquid water again.
Water can also exist as a gas or as a solid. As temperatures decrease, the
constantly changing positions of the water molecules slow, and if temperature
continues to decrease, all possible positions for hydrogen bonding will be
occupied and molecular motion stops - ice formation.
Water and energy
flow downhill, or from high concentrations to lower concentrations. When
ice forms in the spaces between cell walls and even in cell walls, liquid water
flows out of the cell and death from dehydration usually
follows in plants that
are not cold hardy.
But if ice does not form, then dehydration may not occur. When temperatures decrease below 0 degrees Celsius, and the water
is pure and quiet, ice may not form. This is called supercooling of water.
When nucleators are present, the ice will form as crystals about each one.
It seems that if energy and water are stored, and that elements are also
essential for life, then there must be some way the tree stores elements.
It is difficult to conceive that growth and other element-requiring processes
receive elements at the time they are required. There must be a storage
process for elements.
in molecules often precipitate when pH increases. This we know for iron,
manganese and other elements. We know also that some elements such as
potassium can be bonded in many chelated-like forms. Potassium is an element
that is absorbed in its pure form. When potassium is in high
concentrations, the electrical resistivity (as measured by a Shigometer) of the
wood is very low. In summer during the growing season, electrical
resistivity in k-Ohms is low. As winter approaches, the electrical
measurements increase greatly. Summer could be in the 8 k-Ohm or 10 k- Ohm
range while winter could be in the range of a hundred, or even higher. If
potassium is a factor in electrical resistivity, then it must be bonded in ways
that prevent its action as an electrolyte.
Elements must be stored and I believe that much of the
absorption of elements occurs in cold soil in temperate climates.
Photos in books
Results showed many active mycorrhizae and root hairs
in soil under cold water covered by ice. Ectomycorrhizae and
endomycorrhizae from cold soil are shown in color in my book, Tree Anatomy.
On the cover of another book, 100 Tree Myths, I have a color photo of
ectomycorrhizae and root hairs from a Pinus strobus. There are
other color photos of mycorrhizae from cold winter soil in
Points. (The link to the books)
Life in cold soil
The mycorrhizae are not only in nonfrozen soil under
frozen soil, but from soil under water that was covered by ice. Further,
many of the mycorrhizae and root hairs at 1,OOOX with a phase microscope showed
abundance of hyphae inside the non-woody roots. The nucleus in a root hair
is at the tip of the cell. Nuclei in all shapes were viewed. Active
nuclei are round and as they age and die, they become spindle-shaped.
I had other people excavate roots and view them under my
dissecting and phase microscopes. The mycorrhizae were always there. My
neighbor who teaches a biology course at the University of New Hampshire
routinely got samples of mycorrhizae for his class from soil under water and ice
from my pond.
Trees are clusters of highly ordered systems; a conglomerate. Each
system requires time, optimum conditions, and a ready supply of energy, water
and elements. Each process takes time. In temperate climates there is just
not enough time during warm periods to have every process of every system
conduct its activeties.
Survival in living natural systems depends on the rate of
adjustment and adaptation to abiotic systems beyond the control of the biotic
systems. Abiotic systems provide space, temperatures, elements, water and
energy. The positions on Earth where these factors exist are very
different, yet life forms have developed in almost every conceivable place,
including ocean vents, to boiling springs, to cavities within deep ice.
It is not difficult to expect processes of some long-term
systems optimizing places and conditions considered not the best for life.
Absorption of elements developed or adjusted to low temperatures. This
then extended the time for a larger cluster of systems to survive. Trees
have always been and still are the most massive, tallest, longest living
organisms on Earth. To be such superior survivors without the benefits of
movement, the tree systems adapted and adjusted to every possible condition
present over a period of one solar year.
Mycorrhizae are organs made up of fungus and tree
tissues. The organs facilitate the absorption of water and elements
essential for healthy growth. Trees have many redundancies, some for
short-term conditions and some for long-term conditions. Root hairs are
finger-like extensions of single epidermal cells that contain very little lignin
in their walls. The cell walls of the epidermis do have cellulose, which
is not the best of boundaries or membranes for absorption of water and elements.
Root hairs are usually ephemeral. They grow as new roots grow and they go
or die as woody roots begin to form a bark that contains suberin. Their
numbers are usually so great that even if they are poor absorbing structures,
they still absorb some water and elements.
Mycorrhizae present a system of synergy. The fungi
receive more and the tree receives more with this association. Mycorrhizae
live for long periods; a year or more. (Note forms that bud.) |
A mycorrhiza starts when a hypha from a germinating spore
infects a newly forming non-woody root. When some fungi infect a root,
they control the further development of that root. Some fungi penetrate
the root and hyphae spread far beyond the root. It is not uncommon to see
some mycorrhizae with hyphae completely wound about the organ. Root hairs
do exist on some mycorrhizae.
The question quickly arises about how fungi can exist in
roots in soil under water. To make sure the roots were from
neighboring trees, samples were collected from streams where only one tree
species was growing. Large woody roots with smaller masses of roots were
dug. The mycorrhizae were on the tree roots, mostly Acer rubrum and
The fungi in roots under water appeared typical for species
close to Glomus - a member of the Zygomycetes. Chlamydospores of
several types were abundant from the winter samples. (The organisms in the
roots could be oomycetes, which are close to water molds. If this can be
shown, then the organisms would be better classified as endophytes. There
is so much yet to be learned.)
Membranes are nature's
discriminators. Membranes keep things in that should stay in and keep
things out that should stay out. When membranes lose their ability to discriminate,
the cell will die. When many cells die, the organism will die.
Membranes and bonds are extremely important. Bonds hold
matter in place and the bonded matter is further kept in place by some membrane.
The basic unit of life - the cells - speaks to this point.
Plant cells have vacuoles and turgor pressure. Animal
cells have neither. Plant cells have a continuous symplast made possible by
plasmodesmata. Animal cells have another means for intercellular
communication called channels.
Root hairs have cellulose as the major substance in their
outer membrane. Fungi have chitin, which contains nitrogen, in their outer
membrane. Chitin must have unique characteristics for absorption.
Fungi have hyphae that grow through a substrate. Energy-yielding
substances, water, essential elements, and vitamins must be absorbed through the
chitin-rich membrane of the hyphae.
The connection of fungi with trees optimizes two absorbing
systems - cellulose in root hairs, and chitin-rich substances in hyphae.
Mycorrhizae with root hairs have both systems.
What determines what stays in and what comes in?
And what drives this process of absorption? No system can start itself.
Respiration starts the absorption process and once started,
concentration gradients and the Le Chatelier principle keep it going.
Trees are multiple systems operating in states of dynamic
equilibrium. There is the appearance of balance or the static state while really
many processes are moving at equal rates in opposite directions.
Many tree processes can be explained by the Le Chatelier principle. Natural
processes move toward a state of balance, but when they do reach balance, they
Yet, as one part decreases or leaves the equation, the
process moves in that direction, again in an "attempt" to establish
An understanding of dynamic equilibrium and the Le Chatelier
principle are essential to an understanding of not only absorption, but many
other tree processes. Remember, balance means no movement; death!
Nitrogen is essential for growth. What pathway operates for entrance
of nitrogen through a membrane into tree roots? And, how does all of this
relate to mycorrhizae being abundant in cold winter soil? Here are some
additional thoughts based on points of chemistry and results of observations
Chemistry behind absorption of nitrogen
Compounds of carbon, oxygen, hydrogen, nitrogen, sulfur and phosphorus
make up about 98 percent of the mass of trees. Carbon, oxygen and hydrogen
come from water and carbon dioxide; but where do the others come from and how do
they get in?
The elements are absorbed as ions. Ions are molecules,
or elements, that have a positive or negative charge. Like charges repel,
and unlike charges attract. Ions move.
Nitrogen enters as nitrate anion or as ammonium cation.
Phosphorus and sulfur enter as molecules bonded with oxygen as anions.
Each element enters in its pure state. Ions of sulfur,
phosphorus and oxygen are big and heavy. In ways I do not understand, the
fungi with chitin in their hyphal walls facilitate the absorption of these ions.
The absorption of phosphorus by mycorrhizae is one of their most important
Nitrate ion has a molecular weight of 62. Ammonium ion
weighs 18. Now back to respiration. Energy from glucose from stored
starch in living root parenchyma cells is made available for tree processes by
respiration. Respiration is an energy - releasing process. Products
of the process are carbon dioxide and water. When some carbon dioxide
dissolves in water, carbonic acid forms. The
acid dissociates to form
hydrogen ions that bond with water to form hydronium cations and bicarbonate
anions. Hydronium weighs 19 and bicarbonate weighs 61. When you add
19 and 61, 80 is the sum. When you add the weights of nitrate and
ammonium, you also get 80! On the tree side of the rhizoplane, the two
ions weigh 80, and on the rhizosphere soil side, the ammonium of 18 and nitrate
of 62 again weigh 80. Coincidence? I wonder.
Back to cold soil and cold water under ice. First,
water. Cold water contains more oxygen than warm water. Oxygen is a
requirement for respiration!
of ice crystals form in minute cavities. Soil does not freeze, but the
water in soil freezes.
IN COLD SOIL
The ice melted when I placed this sample under the microscope.
The sample came from soil that had ice crystals in the cavities. The soil
came from my back yard in January. The soil surface was covered with snow.
I believe that mycorrhizae and many other organisms do not freeze, but supercool.
In soil below 0 degrees Celsius, clusters of ice crystals
form in minute cavities. In a sense, soil does not freeze, but the water
in soil freezes. That is not as important as the fact that cold soil will
have many ice clusters. I believe the ice clusters in soil act in a way
the sheets of ice over water.
Plants that are not cold hardy die from dehydration because
water moves out of the cell, because water moves from high concentrations to
lower concentrations. As ice forms in soil, liquid water moves toward the
ice clusters. The abiotic cold factor then acts as a trigger for molecules
to move. It is fascinating to know that light heat from the sun triggers
processes that make life possible - photosynthesis. And, low temperatures also
trigger life processes.
As water moves toward ice clusters, air with oxygen fills the
cavities. Many living organisms - bacteria, fungi, mites, thrips, nematodes,
enchytride worms, amoebae -live in the oxygen-rich cavities. And, roots
live there also. Abiotic factors trigger biotic processes!
The rhizoplane is the boundary between soil and living roots
and hyphae. The mycorrhizae serve both tree and fungus. In roots in
soil under water, I believe the endomycorrhizae benefit from the ready supply of
carbon from the tree. In ectomycorrhizae, I believe the fungi and tree
benefit from absorption through a chitin-rich boundary. I believe also
that hyphae that grow out from mycorrhizae obtain some carbon from decomposing
wood and leaves.
Trees, as all living things, pay taxes. Taxes are paid
in the sense of exudates that contain carbon. Many soil organisms benefit
from the "taxes" and in return the organisms make elements available for the
trees. The words of Galileo come to mind as he was faced by his
inquisitors. Galileo said God wrote two books - Nature and Scriptures.
The problem, he said, was that few people have ever read or know about the book
of Nature, and until Book 1 is understood, Book 2 will never be understood.
They did not understand what he said. They issued his sentence! (I
am now working on Book 1.)
Natural systems have developed in ways that benefit
high-quality survival. Systems in tropical climates are different from
systems in temperate climates.
Back to rhizoplanes and the 80, 80 idea. Respiration and the Le Chatelier
principle work to keep the processes moving. The natural "attempt" for balance
keeps getting disrupted as one part of a two-part system keeps moving to a
decreasing state. For example, to move or be absorbed into a root, the
molecule must be in a soluble ionic state. This state is soluble in water
also, and as water moves in soil, the ions move along with the water away from
the target living system. To say it another way, the same ions essential for
life also move "downstream" to the groundwater or on to the ocean, where new and
different life forms exist. Indeed, the natural systems function to
maintain life and non-life, and these processes go on, and will go on, without
the intervention of humans. This is what Book One is all about.
"Always" is what I believe in. Where does a circle start? I
believe that philosophy is a mental trip around a circle. Always.
Life forms and abiotic forms move toward balance. When
balance is reached, the nature of the form changes; death. When abiotic
forms become so highly ordered, we call the resulting form "living." When
living forms become balanced, we call the resulting form "dead."
So long as movement is ordered, life goes on. Dynamic
equilibrium gives nonmoving forms, such as trees, the appearance of balance,
while actually many systems are moving.
Nature is a super, multiple system made up of what we call
living and nonliving forms. Forces external to Earth - the sun - initiate
processes of life and death.
When these powerful forces begin to be recognized, then many
parts will come together.
In the end Modem Arboriculture will come, albeit slowly,
mainly because old arboriculture is accepted by many people and organizations as
it assures economic gains. A new train is coming. It is filled with
students who have different ideas and values for life. This train includes
the quest for solutions that can only come from biology and Book 1, chemistry.
The train is called Modem Arboriculture. It runs on the
energy of connections.
The lack of knowledge of tree biology has been, and still is,
the major problem for trees and tree workers worldwide! Learn about trees.
Connect with nature. Touch trees.
lecturer and consultant, Dr. Shigo started
Shigo and Trees, Associates
years ago after retirement from the U.S. Forest Service.”
Reproduced with permission of Tree Care Industry and Dr. Alex L. Shigo.
The article was published in Volume XIII, Number 12-December 2002 of TCI.
This site is dedicated to the remembrance of Robert Felix who for many years
worked very hard for the improvement of the tree care industry: 1934-1996.
The images for this article were taken from a new CD set that features more than 5,000 items taken from Shigo's research and travels worldwide
over a 40-year period. The CD set has more than 100 chapters with
more than 5,000 color photos.
To order contact
Shigo and Trees, Associates LLC.
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