Make Room for Mycorrhizae!
Monday, April 12, 2021 | Susan Parent
Over the past decades, there has been a growing interest amongst plant scientists in the field of beneficial soil organisms. Studies have shown that many of these naturally occurring bacteria and fungi help plants combat diseases, locate nutrients and acquire water when in short supply to improve and enhance plant growth. This has led to the capture and culture of various beneficial organisms hat consumers and growers can use to inoculate and enhance their crops.
Within the beneficial organism family exists a complex group called mycorrhizal fungi. These fungi grow in association with most plants and have been identified as growth and quality enhancers for many crops. Most mineral soils contain mycorrhizal fungi, but often at levels that are too low for adequate colonization, especially in depleted soils such as tilled fields, newly planted gardens, over-worked landscapes and in new housing development plots.
Mycorrhizal fungi are host-specific and will only colonize certain plants. This means that in some soils, there may no longer be native mycorrhizae present to benefit what you’re about to plant. Therefore, most plants benefit from the addition of mycorrhizae to the soil, while in growing media, adding mycorrhizae becomes even more critical. Most soilless media are composed of peat, coco coir, perlite, bark and expanded clay pebbles that are void of mycorrhizal fungi. This means that plants cannot benefit from mycorrhizal fungi unless they are incorporated into growing media.
Mycorrhiza (singular) is a term that means “fungus root” and describes the mutually beneficial, symbiotic relationship between fungi and plant roots. Symbiosis begins when fungal spores germinate and emerging threadlike structures called hyphae enter the epidermis of plant roots. After colonization of the roots, the fungus sends out a vast network of hyphae throughout the soil to form a greatly enhanced, absorptive surface area (Figure 1). This results in improved nutrient acquisition and uptake by plant roots. Mycorrhizae are particularly effective in mobilizing elements like phosphorus, zinc, manganese and copper. In exchange for nutrients, the plant provides carbohydrates for the fungi.
Figure 1. The thick structures in the picture above are plant roots, while the thin,web like structures are the hyphae of endomycorrhizal fungi. Source: Premier Tech
There are more than 150 species of mycorrhizal fungi found around the world in all types of soils and climates. There are several general classes used to categorize mycorrhizal fungi, but the two most common classes are called ectomycorrhiza and endomycorrhiza. Endomycorrhizae are the most beneficial for herbaceous greenhouse-grown plants. So, how exactly do they benefit plants? Endomycorrhizae help plants by reducing symptoms associated with stress. These benefits of growing with mycorrhizae include:
Reduced nutritional deficiencies
Endomycorrhizae explore the growing medium where plant roots are not present, acquiring nutrients like phosphorus, copper, manganese and zinc. Then they deliver the nutrients they find to the plants to minimize nutrient deficiencies (Figure 2).
Figure 2. The plants on the right were grown with MYCORRHIZAE, while the plants on the left were not. Notice that those grown with MYCORRHIZAE are larger and greener showing the enhanced uptake of nutrients by MYCORRHIZAE. Source: Premier Tech
Reduction in fertilizer use
Since endomycorrhizae explore the growing medium for fertilizer elements, many growers find that they are able to reduce fertilizer application rates. Mycorrhizae make better use of nutrients found throughout the growing medium.
Endomycorrhizae acquire water from the growing medium where plant roots may not be able to access it. This additional water acquired for plants delays or prevents wilting from water stress.
When plants obtain the nutrients they need, they maintain their optimal growing rates longer. Therefore, overall plant growth is improved (Figures 3 and 4).
Figures 3 and 4. In both pictures, the plant on the left was colonized by MYCORRHIZAE, while the plant on the right was not. Notice that in the lettuce (in left picture) and cucumber (in right picture) there was growth enhancement as a result of the MYCORRHIZAE. Source: Premier Tech
Resistance to salt toxicity
Numerous studies have shown that endomycorrhizal fungi protect plants from high-salts in the soil and micronutrient toxicities.
Reduced root disease attacks
Endomycorrhizal fungi make plants less susceptible to attack by root-rot pathogens. They do so in two ways: First they compete against root-rot pathogens by consuming root exudates such as carbohydrates. Second, they help thicken the cell walls of the root cortex, making pathogen penetration more difficult.
Increased fruits and flowers
Since plants grow to their fullest potential with endomycorrhizal fungi, they produce more vegetables/fruits per plant, and/or larger vegetables/fruits. Flowering plants often produce more flowers. Overall, plants often grow more vigorously when colonized by endomycorrhizal fungi, especially if they have been planted into poor-quality, low-fertility soils.
In summary, endomycorrhizae assist plants by enhancing plant nutrient and water uptake, reducing environmental stresses and improving the overall growth of plants. When plant roots form an association with mycorrhizal fungi, the mycorrhizae remain with the plant for its entire life and provide continuous benefits. Numerous studies have demonstrated benefits for plants used for land reclamation, landscape installations and home gardening and for farmers of fruit and vegetable crops, and growers of greenhouse/nursery crops. These benefits contribute to improved efficiencies in plant production and reduce plant production costs for growers.
For more information about mycorrhizae, contact your Premier Tech’s Grower Services specialist:
Jose Chen Lopez
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