Almost all of our horticultural problems,
including insects and diseases, can be explained by looking at
these questions:
 Is
the plant in the right soil?
Is
the plant watered properly?
Is
the plant in the right plant community?
Is
the plant in the right exposure, eg. sun or shade?
Those four questions relate directly to the
plant's roots to support the soil community. On most sites there
is at least as much going on under the ground as above it, and
usually this is more important.
Fungi bacteria and plants all interact and
each plays an essential role in the survival of the others.
The microfungi (mildew, rusts etc.) and macrofungi
(fungi with easily visible fruiting bodies) are the part of foundation
of a native community, with most other microorganisms feeding on them
or with them (associated bacteria and fungi). The driving force of the
fungal community is the plant community, but the plant community cannot
survive if the fungal community is not happy or there at all. Picture a
a house made of round rocks, without some steel(plants) and
cement(fungi) the house would be a pileof rocks.
Most (97%?) of our native plants have to have a
mycorrhizal relationship to be stable in all environments. This
symbiosis can be with many fungi at a time.
Plant communities are closely associated with fungal and
bacterial communities in their soil
 Many
of our native plant communities have nutrient strategies that lock
up the minerals of a site into the leaf litter (mulch), or cycle
it in a closed system, making it available only to themselves and
their allies (other members of their plant community). They do
this with mycorrhizae, not with roots. They have a smaller root
system than seems possible because of the fungal associations. The
mycorrhizal network is nearly invisible to us but is larger by
many times than the bulk of the plant's roots. This is one reason
why in many of our California plant communities, dominated by
obligately mycorrhizal plants, few annual herbaceous plants occur
under the mature plants (including grass) when the community
reaches its climax state. They simply cannot compete and mostly
only exist naturally in the early successional stages. Note: this
situation can be quickly changed with soil disturbance, or
frequent fires with post-fire seeding. This climax state of
affairs is very fragile, and can be quickly destroyed by
disturbance, followed by invasion of alien plant species that are
not part of this system.
Mycorrhizal fungi allow the plant to withstand more stress
Mycorrhizal roots increase drought tolerance by
both finer root like structures, (more soil volume is exploited), and increased
desiccation tolerance (plant roots are thicker and more resistant to
desiccation damage). That is, mycorrhizal roots develop more
stress tolerant structures from the beginning. Sounds
contradictory, but the plants roots become tougher as the attached
fungal hyphae become more numerous and replace root hairs.
The better we understand the symbiosis, the further
the interlinks can be traced in the plant, animal, fungi and now even
microfauna-bacterial community. On harsh sites it's
neccessary to stabilize the site at all levels to make it work
well long term. Most of the research along these lines has been
discovered in only the last few decades.
Healthy soil smells good! Encourage the good organisms in the
soil.
 Build
a native garden right and the microorganisms are stable and happy.
Along with the mycorrhizae are associated soil bacteria that are
nearly as important. Encourage the good ones (that live in the
sweet smelling garden or forest soil good gardeners know) and
discourage the bad ones (that live in the soil that has no smell
or smells like musty newspapers, sauerkraut, or has a sharp acrid
smell ). Smelling soil is as old as farming and has been a very
reliable technique. That's very unscientific but it kinda works. (Lynch
talks about Trichoderma, a common soil fungus, having a
volatile antibiotic that smells like coconut and he points out
volatile antibiotics would make excellent soil fungicides.)
Associated soil bacteria have been found to stimulate root and
mycorrhizal formation. The healthy soil fungi form growth
regulators that inhibit root growth of all plants insuring that
mycorrhizal plants with their fungi (and own growth regulators)
that have a hyphal (fungal roots) system can out-compete the
non-mycorrhizal plants. That is, in a healthy soil roots are told
to slow their growth down, this very much favors our mycorrhizal
natives over ruderals. The rhizosphere (the area of the root where
the fungus-bacteria-soil come together) community, in a healthy
mycorrhizal state secretes, into their host's roots, auxins
stimulating growth of the plant. The fungus tells the plant it is
connected and to grow. The plants roots work the same way with the
fungus, emitting a chemical that tells the mycorrhiza grow. The
healthy root-fungus makes for healthy bacteria that give off
chemicals that also tell the fungus to grow and germinate. If the
bio-balance is shifted with water, fertilizer, etc. the pathogenic
fungus and bacteria replace the desirable ones. The desirable
native fungi in the soil will suppress the pathogen fungi if
allowed too.
Having said all that, agricultural soils also smell good, but you're
smelling free living bacteria and fungi, a different system than a
native system, but one that the agricultural crops want.
 Mulch
is important in a native system!(GOOD)
In ectomycorrhizal and ericoid systems mulch supports this
infrastructure. In VA based systems mulch moderates the moisture
allowing the mycorrhizal plants to be more healthy. The opposite can
also happen. If you cover a site with non-mycorrhizal ruderals or
antagonists (against the mycorrhizal grid) such as rye grass, or
mustard, the good fungi and bacteria will be suppressed or killed
(BAD). The rye grass or mustard will cripple the grid, crippling the
plant community, replacing it with weeds and bad bacteria. Think of
these non-mycorrhizal plants as mistletoe and the mycorrhizal grid as a
tree. The tree can handle minor amounts of mistletoe, large amounts
will kill(decouple) it. Planting large numbers of plants that become
mycorrhizal only to draw moisture and nutrition from the grid (such as
rye) or antagonists (such as mustard) can destroy an ecosystem.(BAD)
These are plants that are normally non-mycorrhizal(ruderals) but can
become mycorrhizal to draw nutrition from the mycorrhizal plants(stress
tolerators). The ruderals are competing with the native plants for
nutrition and moisture during the growing season and drawing from the
biosystem simultaneously. In the summer and fall months when the
natives need to tap into the mycorrhizal grid, to draw back
carbohydrates, the natives find all the reserves are gone. The weeds
have gone to seed with the energy the weeds used from the biosystem.
The energy the weeds had used is tied up above ground in the dead stems
of the ruderals. (BAD) The site is destroyed literally from below the
ground, up. (See
the Disease section.)
For years we couldn't figure out why all the
books, our biology classes, articles, etc. talked of pearly white
roots. There are only a few species in the nursery with pearly
white roots. Although you cannot always tell if a plant has
mycorrhiza/friendly bacteria on it by visual means, there is a
general trend for only the non-mycorrhizal plants to have pearly
white roots. This is apparent when weeds come up in a pot with a
native plant. Weeds have white roots, natives usually have yellow,
red, tawny, brown or black roots. If the weed is allowed to stay
in pot, the native plant will usually die.
Mature natives can suppress weeds; young native
plants cannot. Gangs in a city can be suppressed by proactive
adults; children have no chance. There are three dominant types of
mycorrhizas, the Ericoid, Ectomycorrhiza and Vesicular-arbuscular
mycorrhiza (VAM). (And the Orchids, but we'll ignore them.)
The Harley's
(as quoted in Fitter) found that the woody plants of Great
Britain are 40% VAM, 20% VAM & ectomycorrhizal, 20% Ecto and
20% Ericoid. California is a little higher in VAM and lower in
Ericoid with Ectomycorrhizae about the same. The Ericoid
mycorrhizas grow in peat bogs or acid soils where there is an
organic soup with low Phosphorus and Nitrogen availability, low
pH, and almost no mineral soil.
More fungus fun
Ericoid mycorrhizas are generally ascomycetes,
occasionally a basidiomycetes will show up. They are the most
advanced at extracting and holding Nitrogen and Phosphorus from
organic matter. They have fair drought tolerance but do best when
they are on the edge of constant moisture. You will find them on
the edge of high elevation or high latitude bogs, under large
conifers in heavy duff next to a water source, in very high
rainfall acid soil areas, next to seeps on the north slopes in
heavily forested areas. (Ericoid mycorrhizas are the exception in
California Natives to our watering and planting regime. They love
a lot of peat and other low nitrogen organic matter worked into
the soil and put on as mulch.) These mycorrhizal plants can
detoxify peat. You can tweak a site to make Ericoids happy and
most other things die by providing moderate moisture and 50-70%
peat moss for soil, with no fertilizer or other amendments. Make
sure the plant is Ericoid before you do this, other plants will
decline and die.
Some California sites with ericoid plants
include: Ft. Bragg area on the acid plain mixed in with the Pines,
sand; above Santa Cruz mixed in with the manzanita, sand; in Big
Sur mixed in with Adenostoma
(of all things), sandstone; in Los Osos mixed with manzanita,
sand; in the Sierras in solid stands near seeps, north slope,
6500', loamy-clay.
California natives that have Ericoid tendencies.
 High
elevation Arctostaphylos
(mostly ectomycorrhizal, poorly Ericoid)
Cassiope mertensiana
Gaultheria
shallon
Kalmia polifolia
Ledum gland. californica (Led. gland. is
mainly ectomycorrhizal)
Leucothoe davisiae (primarily Ecto)
Phyllodoce emper.
Pyrola species
Rhododendron
(may also be ectomycorrhizal in California Natives)
Vaccinium
spp.(Vac. ovatum is normally ectomycorrhizal)
Ectomycorrhiza is the second type of fungal
association.
It is sometimes dominant amongst shrubs and
trees in our Mediterranean climate where the rainfall is above 10
inches (30 cm), winter wet, summer dry. The plants that use
ectomycorrhizal are under intermediate nutrient stress or seasonal
nutrient stress. In our state the winter rains provide a specific
bacterial haven for the limited breakdown of the litter in early
winter and early spring, providing a small amount of nutrients.
The ectomycorrhiza are active in most soils at these times when
this nutrition is available to them. They are excellent at
extracting the nutrients from the litter as it is being made
available. (see
Mulches) This litter in the wild may only be one cm. (1/2")
thick. That cm. will contain the limiting nutrition for that site
and provide the site protection from diseases.
It takes about 6-8 weeks before the
ectomycorrhiza become functional on new roots. As ectomycorrhiza
become functional they release a chemical (IAA) that encourages
rooting (on them, not on other plants). What normally happens in
mulched plantings is minimal top growth for a few months to a year
after planting, then the plant grows fast. The young plant expends
its energy for the first months on root growth and mycorrhizal
establishment and has not accumulated enough auxin to stimulate
top growth. One Arctostaphylos
glandulosa was dug out of the demonstration garden because it
was planted in the wrong spot, the roots had grown 1" in 10
days. (the root ball itself should have ectomycorrhiza present.)
Other native plants have been moved after a year (they generally
died after transplanting), and the root ball from a gallon plant
is normally 3 feet across and deep.
It appears that many of our California plants
have the ability to be both ectomycorrhizal and ericoid and/orVA.
These plants serve as energy bridges/shunts in an ecosystem. The
best examples of this are the oaks,
willows,
cottonwoods,
currants,
Rhamnus
species, roses
etc.. These plants act as bridges between water sources and
dry hillside, different soil levels, different plant strategies
and between different plant communities.
Genera of California natives reported on which Ectomycorrhiza
has been described [condensed to just California natives]
*Starred items are most likely to have
ectomycorrhizal native forms.
The others
can be either ectomycorrhizal-Ericoid, ectomycorrhizal-VAM, or
sometimes straight VAM. They will sometimes change as the soil
they are on changes or more often, as the community changes in
maturity or composition.
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Trees in the Abies,
Picea,
Pinus, and
Quercus
genera have to have their ectomycorrhizal associates to survive a
site. These species will out compete all other species in their
environments. Other genera (Cupressus,
Juniperus,
Salix,
Betula,
Corylus,
Alnus, and
Acer) can
survive as long as any ectomycorrhiza are present. It is probable
that as the research continues we will find many, many more
species of California Natives are obligately ectomycorrhizal, some
are semi-parasitic through mycorrhizal associations (Galium sp.
comes to mind), and some can be supported only on certain sites by
certain mycorrhiza. (We've been pushing into the propagation of
many of these species and finding how to overcome the barriers of
site specific mycorrhiza.)
Non-native plants that can also be ectomycorrhizal (They might
also sometimes be VA and sometimes they are not supported by our
mycorrhiza.):
Abies, Cistus, Jacaranda, Picea, Pyrus, Tilia,
Acacia, Crataegus, Juniperus, Pinus, Rhododendron, Tristania,
Carya Cupressus, Larix, Platanus, Ribes, Tsuga, Cassia,
Eucalyptus, Leptospermum, Prunus, Robina, Ulmus, Cedrus, Fagus,
Malus, Pseudolarix, Rosa, Vicia, Celtis, Fraxinus, Melaleuca,
Pseudotsuga, Sorbus, Vitis, Helianthemum
Generally, if the plant is Ectomycorrhizal or
Arbutoid mycorrhizal they need to be mulched for the mycorrhiza to
be stable. Arbutoid mycorrhiza is another type of mycorrhiza and
only forms on some of the genus Arctostaphylos, Arbutus and a few
Rhododendron spp. There is some dispute as to its identity. It may
be only a funny ectomycorrhiza. The arbutoid fungi are
basidiomycetes and are also called ectendomycorrhiza. We treat it
here as ectomycorrhiza as we have found in our installations they
are interchangeable as long as we plant by community.
The more fungi the better!
We believe that it is ecologically more sound
if a mixture of ectomycorrhizal fungi were present on the
seedlings and in the soil. We believe as Dr.
D. H. Marx states "The ultimate objective should be to
have as many good fungi-forming ectomycorrhizae on trees in the
field as possible. This should ensure that as environmental
conditions change during the year (e.g., temperature and rainfall)
the trees will consistently have a physiologically active root
system essential for them to maintain acceptable vigor."
Monoculture is inherently unstable whether it be plant, animal or
fungus.
 As
the plant community matures the mycorrhizal associations also
mature and change. I think it is hard to match the perfect single
mycorrhizal partner for each site. If there are any mycorrhiza on
site, those, along with a number of viable associations on the
container grown stock should be encouraged. If your plant has only
one mycorrhizal partner, it will be without mycorrhizal protection
when the fungus goes dormant during its yearly dormancy.
Valdes found
that having other fungi in the mix with the ectomycorrhiza
increased the survival of the out planted seedlings from 72% to
84%. Our own success has been consistently about 99.5% with
natives. (So good that we could for 15 years as a landscape
contractor unconditionally replant for free any plant that failed
for the first year.) Without any stable mycorrhiza the success was
only 25-50% on these bad sites, no matter how much you watered or
fertilized. (That is what our customers have told us before they
shifted to our stock and methods.)
The other main type of mycorrhiza is
Vesicular-arbuscular. This is usually shorthanded into VA
mycorrhiza or VAM. VAM is present in most root systems except the
family Brassicaceae (even some of those in California).
VAM excel where there is adequate Nitrogen but
limited Phosphorus on mineral soils. They benefit from rock mulch.
If you get too much water, Nitrogen or particularly Phosphorus the
VAM is excluded from the root and the plant loses the mycorrhizal
half of its root system. Fungi that form VA can't function well
alone, they need a host (live plants or recently detached roots)
to provide part of their DNA.
VA mycorrhiza (except desert ones) tolerate
manures, mulch and green manures well, and can even be stimulated
by the increased aeration and fertility of the site. VAM are not
as efficient as the other types at pulling nutrition and water out
of a bad environment, nor do they shield the plant as well from
harsh elements such as the heavy metals. The plant (Like Atriplex)
may overcome this problem in other ways but we have found that
often the ectomycorrhizal is easier to establish than the VAM or
Ericoid(if ectomycorrhizal is present naturally). VAM seem to need
a little better site nutrition than ecto.
 Some
VAM compensate for this inability to pull nutrition and water out
of a bad environment, by having fungi and bacteria in their roots.
The actinomycetes (bacteria) fix nitrogen, the VAM (fungi)pull in
needed Phosphorus for the fixation. The nitrogen fixers will not
develop their root nodulation at all if there is adequate nitrogen
nutrition. Any extra Nitrogen fertilization is too much. VAM
plants tolerate much poorer sites than any garden plant and can be
more drought tolerant in the desert than ectomycorrhizal plants
through a combination of other factors, including a greater
alkaline tolerance. In other words, if the site has ample
nutrients, and regular water (even if it is only 3-7 inches/year)
it will probably be a home to VAM. If it has poor nutrition,
(forest floors look very fertile, but as it is being discovered in
the rainforests that the worst soils are nearly nutrient free and
have ectomycorrhizal trees) and rainfall greater than 10 inches it
will be ectomycorrhizal. VAM likes mineral soils, ectomycorrhizae
likes mineral soils with mulch, ericoid (Rhod., Azaleas, etc.)
likes highly acid, organic, low clay content soils with a constant
moisture source. Most genera in California will be VAM if they are
not Ectomycorrizal or Ericoid, but here are a few examples of
plants that host VAM to show the diversity that can be found in
the literature: Armeria,
Asclepias,
Aster,
Astragalus, Atriplex
canescens and
polycarpa
, Brodiaea,
Carex,
Ceanothus,
Chlorogalum
pomeridianum, Clarkia
purpurea, Cornus,
Dicentra
formosa, Epilobium,
Eriogonum
fasc.,
Eschscholzia,
Eurotia
lanata(Ceratoides),
Festuca,
Fouquieriaceae, Gilia
tricolor, Grayia
spinosa, Lonicera,
Lotus,
Mahonia,
Opuntia,
Orthocarpus,
Poa,
Rosa,
Solidago,
Sorbus, Stipa,
Suaeda,
Thuja
, Viola,
Yucca
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