Super Feeding: Do Mycorrhizae Have a Role in Hydroponics?
The seemingly magical properties of mycorrhizal fungi (aka ‘mycorrhizae’) are already fairly well known to soil growers. This special “root fungus” forms a mutualistic relationship with the roots of many plants, allowing them to access more water and nutrients. Mycorrhizae effectively extend the reach of the roots by forming a mycelial network that is able to extract tightly bonded water and nutrients (particularly phosphorus and iron) and translocate them back to the plant. The plant, in turn, feeds the root fungus with carbohydrates. Everybody’s happy – it’s mutual after all!
Ok, so that’s soil. But what about hydroponics? Nutrient manufacturers remain divided on the issue. Some recommend a completely sterile environment. That means no bacteria (beneficial or otherwise) and no friendly fungi. Why? Proponents of sterile growing environments argue that in hydroponics the grower is supplying all the nutrients their plants need in a directly accessible form and question the need for little ‘fungi helpers’ to assist in nutrient assimilation. (In hydroponics, all the nutrients are supplied in ionic, or directly accessible, form.) Similarly, the roots shouldn’t have to go out in search of water in hydroponics as it’s being provided in abundance. However, recent studies have shown that mycorrhizae can help plants uptake mineral-based nutrients too, promote with root branching, and massively extend the active feeding capacity of the feeder root tips.
Sound interesting? We thought so! So we asked mycorrhizae experts Mike Amaranthus PhD and Josh Eagan BS to give us the low-down on how this special root fungus behaves in a non-soil environment.
Fungus has a bad name going back a long time. The ancient Romans had a legend regarding a malicious boy who tormented a fox by tying wheat straw to its tail and then setting the straw on fire.The Roman god Robigus was so irritated that he penalized humanity with wheat rust, the fungal disease that leaves a farmer’s field looking as though it has been burned. For hundreds of years afterward, the Romans sought to pacify Robigus through sacrifices of dogs and cows with the misfortune of being born with rust-colored fur.
Modern hydroponic growers sacrifice too, increasingly by sacrificing plant quality and profits to prevent damage from a host of fungal “fiends” with names like black rot, club root, sclerotina blight, wire stem, sudden death syndrome, brown spot, and charcoal rot. Opportunities for using beneficial fungi as “friends” exist for the grower as well. The best documented friendly use is mycorrhizal fungal inoculum for improving plant nutrient uptake, plant quality, yields, and disease resistance.
THE FUNGUS FIEND
Most growers blame their nutrients when things start going horribly and unexplainably wrong. Big mistake! Pythium and phytophthora are two of the most common fungal diseases that can affect indoor growers, and they are not easy to spot until well advanced. Pythium-caused root rot is a real problem in hydroponic systems and is becoming increasingly common.
Pythium is a waterborne fungus and recirculating hydroponic systems provide it with an ideal environment in which to live and breed. Plants can survive and grow with high levels of pythium spores in the nutrient solution. The fungus, however, will restrict the root system. A sudden rise in temperature will find the plants unable to increase their uptake of water and they will wilt. For many growers this is the first sign that pythium is active in their system. Damping-off caused by pythium affects growers growing in flats or in the propagation of cuttings. Damping off can attack and topple plants in just a few days. The lower stem becomes constricted and dark brown near the growth media’s surface, a symptom called wire-stem. The hydroponic grower can encounter pythium at any time and, if he is unprepared, he may well lose his crop. Pythium root rot can be caused by several different species of the fungal genera pythium.
Phytophthora, the notorious fungus that caused the Irish potato famine, causes annual crop losses in the tens of billions of dollars today. Beginning in 1845 and lasting for six years, the potato famine killed over a million men, women and children in Ireland and caused another million to flee the country. Phytophthora, from the Greek phytón (“plant”) and phthorá (“destruction”), is literally “the plant destroyer” that continues to plague a wide variety of crops globally with no effective means of chemical control.
Certain fusarium fungal species are also among the most dangerous root diseases in the world affecting hydroponic growers. There has been a dramatic increase in fusarium infection in the last several decades. The ability of this disease to form toxins that are poisonous to both humans and animals makes it a serious problem. The most visible symptom of these fungal diseases is in the root systems. Roots will begin to go brown and lose their healthy white appearance. As the pathogen spreads, the roots become soft and mushy and there is always a tendency for the plant to wilt in the warmer part of the day.
THE FUNGUS FRIEND
We can never purge the world of fungus, of course; nor would we choose to. Fungi represent a kingdom unto themselves, the fifth kingdom in fact. As a taxonomic dominion, kingdom is as high as it gets; animals, plants, bacteria, protists and our fungal friends make up the five.
Some 100,000 species of fungi have been described scientifically, and experts estimate that over a million remain to be discovered. Fungi have influenced our life in ways we take for granted. For a loaf of bread and a jug of wine we can thank the fungus saccharomyces, which is used in bakers’ and brewers’ yeasts. For recovery from infection we can thank the common soil fungus penicillium. Serendipity often leads to fungal discoveries. When Alexander Fleming discovered penicillin, he was trying to perfect an antiseptic formula based on nasal mucus. The nasal mucus formulation never did materialize (we can all breathe a sigh of relief!), but his unforeseen discovery of antibiotics changed the world.
Fungi also have a flair for symbiosis, for establishing cross-kingdom relationships that feed the fungus sugars while bestowing upon its partner new powers. Under natural conditions plants live in close symbiotic association with a group of soil organisms called mycorrhizal fungi. These fungi colonize plant roots and extend the root system into the surrounding soil. Estimates of amounts of mycorrhizal filaments present in growth media associated with plants are astonishing. Several miles of filaments can be present in less than a thimbleful of soil.
The relationship is beneficial because the plant enjoys improved nutrient and water uptake, disease resistance, and superior survival and growth.
It is this not-so-glorious association between plants and mycorrhizal fungi that keeps the whole show rolling in natural environments and can be an important tool for hydroponic growers. Approximately 90 per cent of all land plants depend on the mycorrhizal fungi that radiate from their roots and feed humbly on their plant sugars. In return, the fungus delivers nutrients to the plant like phosphorus, calcium, nitrogen, iron and life-giving water.
The mycorrhizal relationship is ancient and fundamental. In fact, in natural habitats, the presence of mycorrhizal fungi on the roots of plants is as common as chloroplasts to the leaves of plants. Botanists believe that plants might never have made the leap onto land some 460 million years ago without the assistance of Robigus and his mycorrhizal assistants.
This mutually-beneficial association between fungus and plant provides the fungus with relatively constant and direct access to carbohydrates, such as glucose and sucrose produced by the plant in photosynthesis. The carbohydrates are transferred from plant leaves to the root tissues and then to the fungal partners. In return, the plant gains the use of the mycelium’s very large surface area to absorb water and mineral nutrients from the soil, thus improving the mineral absorption capabilities of the plant roots. Mycorrhizal mycelia are much smaller in diameter than the smallest root, and can explore a greater volume of soil-less media, providing a larger surface area for absorption. Also, the cell membrane chemistry of mycorrhizal fungi is different from that of plant roots. The whole length of the mycelia is capable of absorption as compared to just the tips of the roots themselves. Plants grown in sterile soils and growth media often perform poorly without the addition of spores or “propagules” of mycorrhizal fungi to colonize the plant roots and aid in the uptake of soil mineral nutrients.
These mycorrhizal fungi are the best understood of the soil microbe families—and potentially the most useful to growers. Nearly all important crops form the mycorrhizal relationship, with notable exceptions including the mustard family, canola, broccoli, and sugar beets. Mycorrhizae attach themselves to plant roots and grow thread-like hyphae out into the surrounding soil, siphoning amino acids, nutrient molecules and water back to the plant. A grower benefits from mycorrhizal inoculation as it increases the effectiveness of added fertilizer and protects the root system from fungal fiends.
How do mycorrhizal fungi protect roots? The source of disease resistance is probably a combination of factors. The mycorrhizal fungus can present a physical barrier to the pathogenic fungus and/or produce antibiotics that limit the growth of the pathogen. Also, mycorrhizal-colonized plants develop more robust root systems that buffer the plant against the impact of pathogens.
It is also possible that the mycorrhizal fungus stimulates the host to produce chemicals that inhibit the growth of any other fungus on the root. In addition, because the mycorrhizal fungus is so adept at capturing nutrients, there are limited resources available for the growth of the disease fungus. Research has shown that, once a root is colonized by a mycorrhizal fungus, it is more resistant to infection by disease organisms.
INVITING A FRIEND TO DINNER
How do you inoculate mycorrhizal fungi to a hydroponic growing operation? Certain mycorrhizal spores (or “seeds”) of the fungus have been selected for their growth-enhancing abilities. The goal is to create physical contact between the mycorrhizal inoculant and the plant root. Generally, mycorrhizal application is inexpensive and requires no special equipment. Growers have at least three options to inoculate with mycorrhizal fungi.
The first method is an incorporation of a granular or powder form of the mycorrhizal inoculant into the growing media before planting. Secondly, the granular or powder inoculant can be placed into soil or soil-less mixes before placing the transplant into the planting hole, or distributed around the root ball after placement. The third option is a water-in drench. A powder is mixed with water, or a liquid is injected into the rooting zone through existing spray devices. In all three methods, all that is needed is for the mycorrhizal inoculant to reach the vicinity of the roots.
Fungi are omnipresent, occupying every ocean, the atmosphere, and the soil on every landmass. While some fungal fiends are “killers,” attacking living tissue they have infested, the vast majority are benevolent and, in many cases, vital to life forms around them. Fungi can be both fiend and friend to the hydroponic grower. While fungal diseases can impact the grower’s bottom line, mycorrhizal fungi can improve hydroponic yields and be a low-cost, natural solution to increasingly expensive chemical and disease control treatments. Certainly, using beneficial fungi in a hydroponic operation is a preferred alternative to the sacrifice of dogs and cows with rust-colored fur to Robigus!
Big thanks to Urban Garden Magazine for this article! You can find the original article here.