mycorrhizal management

8/7/2019 Mycorrhizal Management

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now believe that the "marriage" of mycorrhizal fungus and plant played anessential role in the evolutionary step which brought aquatic plants from sea to

land. At some point in the evolutionary process, a filament penetrated into theouter cells of a primitive plant root. Once there, it accommodated itself so nicelythat a new, more complex entity emerged, the mycorrhiza. The increased

absorbing area provided by an elaborate system of fungal filaments allowed

aquatic plants to leave the marine environment and exploit a relatively harsh soilenvironment. In today's man-made environments plants can be greatly stressedand the relationship between fungus and root is critical. Unnatural conditionssuch as concrete, asphalt, roadsides, sidewalk cut outs, trenching, drain fields, air

pollution, shopping malls, business districts, and suburban developmentsadversely affect the presence and abundance of mycorrhizal fungi.

Man-made environments often suffer fromcompaction, top soil loss, and the absence of qualityorganic matter, conditions which reduce the habitatnecessary for the mycorrhizal fungus to survive and

thrive (Figure 3). Artificial landscapes effect themycorrhizal relationship in two fundamental ways.First, they isolate the plant from beneficialmycorrhizal fungi available in natural settings and,

secondly, they increase plant stress and the need for water, nutrients, and soil structure mediated by their

below-ground "partners".

Fortunately, recent advancements in mycorrhizalresearch and application have made landscapeapplications with mycorrhiza easy and inexpensive.

New products and knowledge result in increasedtransplant survival and lower long-term maintenance.However, to be successful the landscape contractor

requires an appreciation of fungi beyond itchy toes and moldy bread.

Figure 3 Construction sitestypically compact the soiland remove organicmatter and topsoil. Thesepractices reduce or

eliminate mycorrhizalfungi.



How do mycorrhizal fungi work?

Mycorrhizal root systems increase theabsorptive the absorbing area of roots 10to 1000 times thereby greatly improving

the ability of the plants to utilize the soilresource. (Figure 4). Mycorrhizal fungi

are able to absorb and transfer all of the15 major macro and micro nutrientsnecessary for plant growth. Mycorrhizal

fungi release powerful chemicals into thesoil that dissolve hard to capture nutrientssuch as phosphorous, iron and other "tightly bound" soil nutrients. This

extraction process is particularlyimportant in plant nutrition and explainswhy non mycorrhizal plants require high

levels of fertility to maintain their health.Mycorrhizal fungi form an intricate webthat captures and assimilates nutrientsconserving the nutrient capital in soils. Innon mycorrhizal conditions much of this

fertility is wasted or lost from the system.

Mycorrhizal fungi are involved with a wide variety of other activities that benefit

plant establishment and growth. The same extensive networks of fungalfilaments important to nutrient uptake are also important in water uptake andstorage. In non-irrigated conditions, mycorrhizal plants are under far less drought

stress compared to non mycorrhizal plants. In a recent study, true fir seedlingstreated with mycorrhizal inoculums had 43 percent less plant moisture stress thannon-treated control seedlings on a droughty, difficult to revegetate site. Treevigor, color and needle retention were improved with the mycorrhizal treated

plants (Figure 5). Rhizopogon mycorrhizae were abundant on the roots systemsof the treated plants (Figure 6). Numerous studies have shown Rhizopogon spp.is an aggressive colonizer in non-irrigated and harsh field conditions.

Figures 5a & 5b

Figure 4 "Cut-away" view of the root structureof conifer seedlings, enhanced andextended by a network of mycorrhizalfilaments.



Red fir seedlings ( Abies magnifica) outplanted on a difficult to regeneratedry site. Seedling A was treated with a mycorrhizal inoculums; seedling Bwas not treated. Treated seedlings averaged 43% less moisture stressand 30% more needle retention.

Disease and pathogen suppression is another benefitfor a mycorrhizal plant. Mycorrhizal roots have amantle (a tight, interwoven sock-like covering of dense filaments) that acts as a physical barrier against

the invasion of root diseases. In addition, mycorrhizalfungi attack pathogen or disease organisms enteringthe root zone. For example, excretions of specific

antibiotics produced by mycorrhizal fungi immobilize

and kill disease organisms. Some mycorrhizal fungiprotect pine trees from P hytophora, Fusarium andRhizoctonia diseases. In a recent University study,pine trees were purposefully inoculated with the

common disease organism- Fusarium. Over 90% of

the pine trees died. Only the pine trees inoculatedwith the mycorrhizal fungus Rhizopogon survived.Survival rates for Rhizopogon treated pines exceeded

95%.

Mycorrhizal fungi also improve soil structure.

Mycorrhizal filaments produce humic compounds and organic "glues"(extracellular polysaccharides) that bind soils into aggregates and improves soilporosity.

Soil porosity and soil structure positively influence the growth of plants bypromoting aeration, water movement into soil, root growth, and distribution. Insandy or compacted soils the ability of mycorrhizal fungi to promote soil

structure may be more important than the seeking out of nutrients.

Does my soil already contain mycorrhizal fungi?

Soils in natural settings are full of beneficial soil organisms including

mycorrhizal fungi. Research indicates, however, many common practices candegrade the mycorrhiza-forming potential of soil. Tillage, fertilization, removal

of topsoil, erosion, site preparation, road and home construction, fumigation,invasion of non native plants, and leaving soils bare are some of the activitiesthat can reduce or eliminate these beneficial soil fungi. In many man-made

landscapes we have reduced or eliminated the soil organisms necessary for plantsto function without high levels of maintenance.

Nursery grown plants available to landscape contractors are often deficient in

mycorrhizae. Plants raised in most nurseries receive intensive care and feeding.The artificial conditions, high levels of water and nutrients and sterile soils at thenursery keep certain soil born diseases to a minimum and produce vast quantitiesof plants for sale. Unfortunately, the high levels of water and nutrients and the

Figure 6 A cluster of R hizopogon mycorrhizae. A singleroot tip colonized by theR hizopogon mycorrhizalfungus will branch into adensely packed coral-likeaccumulation of manyroot tips.



lack of mycorrhizae discourage the plant to produce the extensive root system itwill need for successful transplantation. The results are plants poorly adapted to

the eventual outplanted condition that must be weaned from intensive caresystems and begin to fend for themselves. Application of mycorrhizal inoculumsduring transplanting can encourage plant establishment and set the plant on track

to feed for itself. Research studies document the need of plants to generate a

mycorrhizal roots system in order to become established. Maintaining intensiveinputs is necessary until the extensive root system is achieved. There arepractical solutions to some of the mycorrhizal deficiencies in man-madeenvironments and reintroducing mycorrhizal fungi in areas where they have been

depleted can dramatically improve plant establishment and growth.

What types of mycorrhizal products are available?

A landscape contractor can enhance plant root growth and transplant success and

ameliorate many problems that result from intensive care practices at the nursery.Plants grew and thrived on this planet for millions of years without intensive

care. Nature provides the template. A more sustainable approach to plantestablishment and growth includes using mycorrhizal fungi.

Certain mycorrhizal spores or "seeds" of the fungus have been selected for their establishment and growth-enhancing abilities. The goal is to create physicalcontact between the mycorrhizal inoculant and the plant root. Mycorrhizal

inoculant can be sprinkled onto roots during transplanting, worked into seed

beds, blended into potting soil, watered in via existing irrigation systems, appliedas a root dip gel or probed into the root zone of existing plants. The type of application depends upon the conditions and needs of the applicator. Generally,mycorrhizal application is easy, inexpensive and requires no special equipment.

Typically for small plants the cost ranges from less than a penny to a few centsper seedling. For larger plants more inoculums is needed and costs are higher.

Mycorrhizal products often contain other ingredients designed to increase theeffectiveness of the mycorrhizal spores. For example, organic matter is oftenadded to encourage microbial activity, soil structure and root growth. Stressvitamins improve nutrient uptake and builds root biomass. Water absorbing gels

help "plaster" beneficial mycorrhizal spores in close proximity to feeder rootsand encourage favorable soil moisture conditions for mycorrhizae to form andgrow. Organic biostimulants, in general are effective ingredients in mycorrhizal

products. By promoting field competitiveness, stress resistance and nutrientefficiency biostimulants reduce barriers for rapid mycorrhizal formation

especially during the critical period following transplanting.

Mycorrhizal diversity is important

Natural areas generally contain an array of mycorrhizal fungal species. The

proportions and abundance of mycorrhizal species often shifts following anydisturbance. Not all mycorrhizal fungi have the same capacities and tolerances.Some are better at imparting drought resistance while others may be more



effective in protecting against pathogens or have more tolerance to soiltemperature extremes. Because of the wide variety of soil, climatic, and biotic

conditions characterizing man-made environments, it is improbable that a singlemycorrhizal fungus could benefit all host species and adapt to all conditions. For example, the types and activities of mycorrhizal fungi associated with young

plants may be quite different from those associated with mature plants Likewise,

mycorrhizal fungi needed to help seedlings establish themselves on difficult sitesmay differ from those which sustain productivity over a long-lived plant.

Diversity likely provides a buffering capacity not found on sites with only one or few species. The diversity of mycorrhizal fungi formed by a given plant mayincrease its ability to occupy diverse below-ground niches and survive a range of

chemical and physical conditions.

Conclusions

The lack of mycorrhizal fungi on plant root systems is a leading cause of poor

plant establishment and growth in a variety of forest, restoration, agricultural,suburban and urban landscapes. As we develop holistic approaches to

understanding man-made environments we must factor in the inseparableconnections to soil organisms. Mycorrhizal fungi are one of the more importantgroups of soil organisms and play a critical role in nutrient cycling, mediatingplant stress and protecting against pathogens. They are also cornerstones in the

ability of plants to survive transplant shock. Plants have co-evolved mutualistic

relationships with symbiotic mycorrhizal fungi such that their survival andfitness depends upon the healthy functioning of these fungi and vice versa. Justas plants invest tremendous capital in the form of energy to fuel below-groundsoil organisms, so too we must "look below the surface´ to understand and

utilize these beneficial fungi.

Dr. Mike Amaranthus spent 20 years with Oregon State University and the US DAForest Service where he authored over 50 research papers on mycorrhizae. He is arecipient of the US DA Department of Agriculture Highest Honors Award for scientific achievement and has been featured on several major national and international television programs.

mycorrhizal management

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