Over the past several decades, there has been a growing interest amongst plant scientists in the field of beneficial soil organisms. These workhorses of the garden can be considered the superheroes of soil, as bacteria and fungi can help plants combat diseases, locate nutrients and acquire water when in short supply.
Within the beneficial organisms 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 in some soils, there may no longer be native fungi present to benefit what you’re about to plant. Therefore, most plants benefit from the addition of mycorrhizal fungi to the soil, while in other grow mediums, adding them becomes mission critical. Take greenhouse-grown crops, for example. They are grown mostly in soilless media that are void of mycorrhizal fungi, so these beneficial organisms need to be added to mediums like peat, coco coir, perlite, bark and expanded clay pebbles.
Mycorrhiza (singular), which 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 hyphae enter the epidermis of plant roots. After colonizing the roots, the fungus sends out a vast network of hyphae throughout the soil to form a greatly enhanced, absorptive surface area.
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 the glorious gift of nutrients, the plant gives carbohydrates to the fungi to snack on.
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 them, but the two most common classes are ectomycorrhizal and endomycorrhizal fungi. For herbaceous, greenhouse-grown plants, endomycorrhizal fungi are the most beneficial. So, how exactly do they benefit plants? It’s simple, really. They help plants endure stressful situations by delaying the symptoms that come with the stress. Other benefits include:
- Reduced nutritional deficiencies. Endomycorrhizal fungi mine the growing medium where plant roots are not present, looking for nutrients like phosphorus, copper, manganese and zinc. Then they deliver the nutrients they find to plants, which prevents or delays nutrient deficiencies in the garden.
- Potential reduction in fertilizer use. Since the fungi mine the growing medium for nutrients, many growers find they are able to reduce fertilizer application rates.
- Delayed wilting. Endomycorrhizal fungi acquire water from the growing medium where plant roots may not be able to access it. This additional water for plants delays or prevents them from wilting due to water stress.
- Improved growth. When plants can more effectively uptake the nutrients they require, they can maintain their optimal growing rates longer, which means top growth and root growth are not compromised when plants are supplied with endomycorrhizal fungi.
- Resistance to salt toxicity. Numerous studies have shown that endomycorrhizal fungi protect plants from high-salt and micronutrient toxicities.
- Reduced root disease attack. Endomycorrhizal fungi make plants less susceptible to attacks by root-rot pathogens. They do so in two ways: first they serve as competition to root-rot pathogens by consuming root exudates, such as carbohydrates. Second, they help thicken the cell walls of the cortex, making pathogen penetration more difficult.
- Increased fruit and flowers. Since plants grow to their fullest potential when supplied with endomycorrhizal fungi, they produce either more crops per plant, or larger vegetables and fruits. Flowering plants often produce more flowers. Overall, plants often grow larger when they are given endomycorrhizal fungi, especially if they have been initially planted into poor-quality, low-fertility soils.
So, endomycorrhizal fungi assist plants by enhancing plant nutrient and water uptake, reducing environmental stresses and improving the overall growth of plants. Numerous studies have demonstrated the benefits for plants used for land reclamation, landscape installations, home gardening, farmers of fruit and vegetable crops, and growers of greenhouse/nursery crops.
These benefits can improve efficiencies in plant production and reduce plant production costs for growers. When the choice comes down to mycorrhizae or no mycorrhizae, it’s plain to see that added mycorrhizal fungi takes the prize every time.