Benefits of Mycorrhizae for growing media

What are Mycorrhizae?
Mycorrhiza (singular), a term that means “fungus root,” describes the mutually beneficial, symbiotic relationship between fungi and plant roots. Symbiosis begins when fungal spores germinate and emerging threadlike structures, called ‘hypha’ (plural hyphae), enter the surface of plant roots. The plant root system and fungal hyphae combine to form a greatly enhanced absorptive surface area. The result is improved nutrient acquisition and uptake, particularly elemental phosphorus (P), zinc (Zn), manganese (Mn) and copper (Cu) and water. In return, the plant provides carbohydrates to the fungi. This root-fungus association mutually benefits the host plant and fungi. There are more than 150 defined species of mycorrhizal fungi found around the world in all types of soils and climates.

Types of Mycorrhizae
There are two general classes that categorize mycorrhizal fungi as Ectotrophic and Endotrophic (commonly called Ecto and Endo). Each classification is based on the inter-relation of threadlike fungal hyphae and the plant root cell.

Ectomycorrhiza form a compact mantel on the surface of plant roots, but do not enter plant root cells. Mycelia strands extend inward between cortical root cells and outward from the mantle to soil surface. Often hyphal fruiting bodies (stinkhorns and other mushrooms) can be seen in forested areas around the base of trees after sufficient amounts of rain. Ectomycorrhiza commonly occur on pine (Pinaceae) and other conifers, birch (Betulaceae), beech and oak (Fagaceae) families and some woody plants. Many forestry tree nurseries use ectomycorrhizae to inoculate conifer seedlings to improve survival when out planted.

Endomycorrhizae form associations on most seed bearing plants, rain-forest tree species, most agriculture crops and a majority of ornamental plants. Endomycorrhizae form an association in which fungal hyphae penetrate the epidermal and cortical cells of plant roots. Endomycorrhizae are present on root surfaces only as individual threads that may penetrate directly into root hairs, epidermal cells and the fleshy cortex cells of roots. Although it is not fully understood, it is possible that recognition signals allow the mycorrhizal fungus to penetrate the plant root tissue. Individual threads extend from the root surface and outward into surrounding soil forming a vast network. This allows an improved absorption of nutrients and water by the root, particularly unavailable or limited amounts.

Endomycorrhizae are invisible to the naked eye and form structures between and within the cortex cells of plant roots. Hyphal branches penetrate the host cell and give rise to small structures called “arbuscules” (Latin for tree). These structures resemble tiny trees and serve as exchange sites within cortical cells of plant roots. Arbuscules form within two to three days after the cell is colonized and will last from one to three weeks. Sac-like structures, called “vesicles” (little sac), are generally found as terminal ends of hyphae filaments. Vesicles contain many lipid droplets and serve primarily as storage organs for the fungus. Vesicles can also germinate into propagules to colonize other portions of plant roots. Normally, vesicles form after the collapse of arbuscules and become more numerous late in the growing season as plants mature. Both arbuscules and vesicles are connected by long threads of fungal hyphae inside and outside the plant root system.

Benefits of endomycorrhizae
Some of the benefits include larger plant size, enhanced foliar quality, more profuse flowering and fruiting, resistance to certain diseases and improved resistance to certain stresses during cropping (transplanting, drought, salinity), particularly when mycorrhizal plants are introduced to poor soils. Endomycorrhizae also make better use of fertilizer and water. Although there are several different genus and species of endomycorrhizae, the most important genus and species for agriculture and ornamental crops is Glomus intraradices. Much research has documented the benefits of Glomus intraradices.

Mycorrhizae for Planting Success
Once plants are colonized by mycorrhizae, they remain with the plant root system and can be transferred into the garden and other outdoor plantings. For average soils, benefits are most evident when plants are subjected to stressful growing environments (i.e.: arid conditions, unseasonable temperatures, low nutrient soils, excessive fertilizer, transplanting, and establishment of new plantings). This is particularly important for growers and consumers who wish to maximize the success of their plants purchased at the garden center.

To learn more about PRO-MIX Professional Growing Media enhanced with Mycorrhizae, visit Premier Tech Horticulture’s website at pthorticulture.com.