All About Mycorrhizae

Mycorrhizal inoculums are the spores of beneficial fungi that the majority of landscape plants and agricultural crops need in order to have optimum health.  Research has proven that when plants are given this beneficial inoculation of mycorrhizae they will become dramatically more drought tolerant, healthier and better able to tolerate the stresses of heat, cold, lack of water and poor soils.  The idea of using mycorrhizal products in ether landscaping or farming is still a new concept, but it is clear that with mycorrhizae, we can grow healthier, more productive and sustainable plants while minimizing and even eliminating the use of toxic agricultural chemicals!     

Is it Mycorrhiza, Mycorrhizae or Mycorrhizal?  The use of these three names has confused the best of us, so for all our benefit heres the proper use of those terms. 

The benefit is a healthier environment that uses less water and fewer chemicals that are harmful to the environment and our bodies.     

Mycorrhiza – a single mycorrhiza Mycorrhizae – plural- many mycorrhizae (mycorrhizas if you are British) Mycorrhizal – adjective, as in mycorrhizal fungi, or mycorrhizal plant. 

Mycorrhizae appear in the earliest fossil record of terrestrial plant roots. Roughly 90% of the nearly 10,000 plant species that have been examined are mycorrhizal. Present-day plants that normally lack mycorrhizae are generally evolutionarily advanced and include many of the worlds more troublesome weeds.  It has been proven that plants evolved with a symbiosis between fungi and rhizoids or roots as a means to extract nutrients and water from soil.  

The degree of dependence varies between species or groups of plants. In absolute dependence, characteristic of perennial, terrestrial plants, the host requires mycorrhizae to survive.   A minority of plant species characteristically lack mycorrhizae, so far as is known, including many aquatics, epiphytes, and annual weeds. 

The three major types of mycorrhizae differ in structural details but have many functions in common. The fungus colonizes the cortex of the host root and grows its filaments (hyphae) into surrounding soil from a few centimeters to a meter or more. The hyphae absorb nutrients and water and transport them to host roots. The fungi thus tap far greater volumes of soil at a relatively lower energy cost than the roots could on their own. Moreover, many, if not all, mycorrhizal fungi produce extracellular enzymes and organic acids that release immobile elements such as phosphorus and zinc from clay particles, or phosphorus and nitrogen bound in organic matter. The fungi are far more physiologically capable in extracting or recycling nutrients in this way than the rootlets of plants themselves.

Research has also shown that these microscopic tubes of mycorrhizae called hyphae can also penetrate rock and super tight soils that plant rootlets are not capable of penetrating.  This in turn increases the contact zone a mycorrhizal plant will have with the terrestrial biosphere we call soil and therefore magnifies the volume of nutrients and water that is accessible to the host plant.   

For food, Mycorrhizal fungi are poorly competent in extracting carbon from the decaying organic matter of soil, so they depend on a host plant for there nutritional needs.  They derive energy from host-photosynthesized carbohydrates. Hosts also provide vitamins and other growth regulators that the fungi need. 

The major types are ectomycorrhizae, vesicular-arbuscular mycorrhizae, and ericoid mycorrhizae. Ectomycorrhizae are the most readily observed type. Ectomycorrhizal hosts strongly depend on mycorrhizae to survive with the host plant being a Mycorrhizal obligate plant. Relatively few in number of species, they nonetheless dominate most forests outside the tropics. Vesicular-arbuscular mycorrhizae (sometimes simply termed arbuscular mycorrhizae or endomycorrhizae) form with the great majority of terrestrial herbaceous plant species plus nearly all woody perennials that are not ectomycorrhizal. Vesicular-arbuscular mycorrhizal hosts range from strongly mycorrhiza-dependent, especially the woody perennials, to the facultative plants such as many of the annual grasses. 

Ericoid mycorrhizae are restricted to the Ericales, the heath order. The hosts are strongly mycorrhiza-dependent. Though relatively few in number, heath species dominate large areas around the world and are common understory plants in many forests. Other mycorrhiza types include those special for the Orchidaceae (orchids) and Gentianaceae (gentians). See also Ascomycota; Ericales; Zygomycotina. 

The succession of plants from pioneering through seral to climax communities is governed by availability of mycorrhizal propagules. When catastrophic fire, erosion, or clear-cutting reduces the availability of mycorrhizal fungi in the soil, plants dependent on those fungi will have difficulty becoming established. Each mycorrhizal fungus has its own array of physiological characteristics. Some are especially proficient at releasing nutrients bound in organic matter, some produce more effective antibiotics or growth regulators than others, and some are more active in cool, hot, wet, or dry times of year than others. Healthy plant communities or crops typically harbor diverse populations of mycorrhizal fungal species. This diversity, evolved over a great expanse of time, is a hallmark of thriving ecosystems. Factors that reduce this diversity also reduce the resilience of ecosystems. 

Mycorrhizal inoculation of plants in nurseries, orchards, and fields has succeeded in many circumstances, resulting in improved survival and productivity of the inoculated plants.  

Inoculation with specific mycorrhizal fungi  and a Probiotic of bacteria is especially important for restoring degraded sites or when installing plant material on sites that have been missing vegetation for a growing season or longer.    

In manmade landscapes, it can be said that almost without exception plants will not be mycorrhizal.  Parks, sports fields, backyard lawns, vegetable gardens, farms and even organic certified farms have all been evaluated across the country and have been found to consistently lack a significant level of mycorrhizal articulation with the plants on those sites.  I personally tested two of the oldest parks in Albuquerque New Mexico to see if the turf and trees had any mycorrhizal relationship and found none existed.  This was despite the fact that these parks dated from the 1930s and have been carefully manicured with beautiful lawns and trees.  In 80 years mycorrhizae have not reestablished in those two parks which also indicates that the plant material growing on these sites will be constantly and consistently addicted to extra watering and fertilizer in order to survive.     

The issue of keeping these parks green in the future may very well be contingent upon making these landscapes mycorrhizal!   


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