Certain micro-organisms and fungii are great for soil.
mycorrhizae help promte healthy, stronger plants with better pest/infection resistance..
Here's an exert from a botanists Phd paper..
When plants live in challenging locations, they often develop mechanisms to help them
survive. These include morphological characteristics such as thickened, small or narrow leaves
to reduce water loss, slowing the plant's growth rate, or developing a tolerance for high salts
and low levels of nutrients. One important set of survival mechanisms involves creating
mutually beneficial (symbiotic) relationships between plant roots and soil-borne organisms
such as bacteria and fungi.
What are mycorrhizae?
The associations between roots and fungi are called mycorrhizae. These symbiotic
arrangements have been found in about 90% of all land plants, and have been around for
approximately 400 million years. Plant roots are hospitable sites for the fungi to anchor and
produce their threads (hyphae). The roots provide essential nutrients for the growth of the
fungi. In return, the large mass of fungal hyphae acts as a virtual root system for the plants,
increasing the amount of water and nutrients that the plant may obtain from the surrounding
soil. A plant that forms an association benefiting both the fungus and the plant is a "host."
Large numbers of native desert plants are hosts to these fungi and would not survive without
them.
Two general terms are used to describe virtually all mycorrhizae:
In ectomycorrhizae (external), the fungus produces a sheath around the root.
This sheath then produces hyphae that grow into the root and out into the soil.
Endomycorrhizae (internal) do not produce a sheath; the hyphae grow within the cells
and out into the soil. These are far more common than the ectomycorrhizae.
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What do mycorrhizae do?
Nutrients and water
Mycorrhizae are essential in areas where soils are deficient in water and certain nutrients -
conditions that are found in the desert. Even when there is an ample amount of a nutrient, it
may not be readily accessible to the plant. A dramatically larger root system (or
mycorrhizae) permits the plant to obtain additional moisture and nutrients. This is particularly
important in uptake of phosphorus, one of the major nutrients required by plants.
When mycorrhizae are present, plants are less susceptible to water stress. Not only do the
fungal threads help to bring water and nutrition into the plant, but they also can store them for
use when rainfall is sparse and temperatures are high. When organic matter (compost) is
added to improve a soil, mycorrhizae are important in making its nutrients available. The
residual organic matter and the hyphae improve the structure of the soil. Recent research
indicates that the fungi even help break down rock, increasing availability of the essential
nutrients within, such as potassium, calcium, zinc and magnesium.
Disease resistance
Mycorrhizae also help the plant resist infection by other fungi and even bacteria. This may be
because the plant, being better nourished, is healthier and has better resistance to the invader.
It may also be that the large physical presence of one fungus impedes infection by others.
Another possibility is that either the plant or the fungus produces compounds that prevent
infection by pathogens.
Interaction with other soil microbes a cycle of benefit
Desert plants interact with other organisms in the soil. Many of these microorganisms fertilize
plants by "fixing" nitrogen, which is then available for plant growth. When mycorrhizae are
present, the number and vitality of these nitrogen fixers increase. As a result, the plants health
and vigor improves, as does the health and vigor of the beneficial fungi.
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Will any fungus form mycorrhizae?
Many fungi will form associations with plants, and many plants will form mycorrhizal
associations. These interactions appear to be plant- and fungus-specific. Not all mycorrhizae-
forming fungi will work with all desert plants. There are research reports which show that
association with the "wrong" fungus actually decreases the health and vigor of the plant.
Because there is a requirement for specific plant-fungus association, mycorrhizae can be
important in reestablishing native species in areas where they have been lost.
Mycorrhizal fungi are available for sale from several sources.
Introducing mycorrhizal fungal spores (inoculation) is sometimes suggested to improve yields
and plant vigor, particularly for container and landscape ornamentals. Inoculation with
mycorrhizal fungi may not be a benefit unless it is specific to the plant, because there is a
requirement for a specific fungus-plant interaction for optimum benefit. It would also be
counterproductive to inoculate with a fungus that could strongly benefit a weedy species.
How do mycorrhizae get into a site?
Many desert soils already have mycorrhizal fungi present, at least in small amounts. Even
without inoculation, spores can be found in many desert locations. If host plants are grown
where there are spores of these fungi, then both thrive. The mycorrhizal fungi may continue to
survive even after the original host is no longer present.
The hyphae enter the root and create swellings (vesicles) for nutrient storage structures
where nutrients are transferred between fungus and plant (arbuscules).
The names of these two structures are combined into "vesicular-arbuscular mycorrhizae"
(VAM), the term for the most common type of mycorrhizal association.
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Maintaining mycorrhizae in the soil
There is no sure-fire way to guarantee natural mycorrhizal populations, but in order to
increase the amount of fungi, follow a couple of basic rules. When planting a desert native,
make sure that the root ball contains native soil. This is where the mycorrhizal fungi reside;
without the fungi, there can be no associations.
Just as important, be very careful when using pesticides, particularly fungicides. Do not apply
them to the soil. Fungicides kill all the fungi they encounter. While they can be effective against
plant disease, they can destroy beneficial fungi and cause serious problems to plant survival.
