Jan. 19, 2016 03:36


page 18 Mycorrhizae

Let’s play word association. When you hear the word “fungus,” what do you think of? Mushroom pizza? That time you had athlete’s foot? If we played this game with a soil scientist, he would probably smile, because to him, the word “fungus” means healthy, green, growing plants.

It’s a particular class of fungi he’d be thinking of, called mycorrhizae, from the Greek word meaning “fungus/roots”. “Mycorrhizal fungus is the most important organism found in soil, and it’s been there for hundreds of millions of years,” said Trent Hreno,  Canadian sales manager for ECB/Verdyol, a wholly-owned subsidiary of ErosionControlBlanket.com, Inc., headquartered in Riverton, Manitoba, Canada.

‘Fungus’ is not just another word for fertilizer. “Fertilizers are nutrients, like nitrogen (N), phosphorus (P), and potassium (K), the N-P-K number on the bag,” said Robert Neidermyer, PhD, director, soil and plant science at Holganix, a soil amendment manufacturer based in Glen Mills, Pennsylvania.

“The N, P and K are the inert chemical elements that are used to grow plants; plants cannot grow without them.”

“If you’ve got poor soil with very little nitrogen or any other nutrients in it, and no mycorrhizae and bacteria either, you have to figure out a way to add them back in, or your plants just won’t do very well,” said Dennis Richmond, owner and CEO of Richmond Hydromulch and Seeding, LLC, Wylie, Texas.  “They might grow, but they’ll look sick.”

“Mycorrhizae and bacteria act as probiotics for the soil,” Neidermyer says. “They’re microorganisms that exist in association with plants and help them function, picking up nutrients and moisture for them.  They aren’t fertilizers, as they aren’t chemicals; they’re actual, living organisms.” In other words, mycorrhizae act as “Fertilizer Helpers,” bringing the nutrients in the fertilizer right to the plants’ roots.

Mycorrhizal fungi is no wallflower; it gets around, establishing a symbiotic relationship with the roots of just about every plant on Earth, including grasses, grains, flowers and trees.

There are two main categories of mycorrhizae: endomycorrhizae and ectomycorrhizae. It’s helpful to remember that the prefix “endo” means inside, and “ecto” means outside.

“The endomycorrhizae literally attach themselves to the roots, penetrate cell walls, and become one with the roots,” said Neidermyer. “The ectomycorrhizae just kind of lay up next to the roots, coming into very close proximity, but don’t attach themselves.”

Of the two players, endomycorrhizae is by far the most popular. “Approximately 80 to 90 percent of all plants in the world form symbiotic relationships with it,” said Hreno. These include a wide variety of green, leafy plants and cultivated grasses, as well as many dryland, wetland, aquatic and riparian species, making endomycorrhizae vital to both greenhouse growers and the erosion and sediment control industry.

Hreno continued, “Ectomycorrhizae, on the other hand, forms symbiotic relationships with only about five percent of all the plants in the world. These are mainly tree species, including pine, spruce, fir, and hardwoods such as oak and birch, making this category of mycorrhizae vital to the forestry industry. Some commercially important plant species also benefit from linkage with ectomycorrhizae.” 

Plants need three things to survive: sunlight, water and nutrients. Mycorrhizae functions as a delivery system for the latter two. The plants and the fungi work together as a single, functioning unit. “The plants perform photosynthesis above the ground, while the mycorrhizae colonize the roots below the ground,” Hreno said. “They send their tiny filaments far out into the soil,” well beyond the roots they’ve colonized. 

Some symbiotic relationships in nature benefit one of the partner species much more than the other one. But the plant-mycorrhizal fungi-symbiosis is an equal union that both sides benefit from greatly.

As the filaments grow and stretch out, they behave like military reconnaissance squads, conducting sweep searches for water and nutrients over a large underground area. Once the water and nutrients are found, the filaments transport them directly back to the roots of the plants. In return, the plants, through photosynthesis, reward the mycorrhizae with the glucose it needs to thrive.

For plants, the major advantage of this relationship is an enhanced supply of available nutrients, including carbon, potassium, phosphorus and nitrogen. They also get a faster uptake of minerals such as calcium, copper, iron and zinc, and in greater amounts, than would normally have been available to their roots.

“The presence of mycorrhizae also gives plants an increased tolerance to adverse soil conditions,” said Hreno. “The plants can continue to grow and do much better than they would without the fungi’s help, even in degraded, nutrient-deficient soils, or soils with lower-than-ideal pH and higher-than-ideal soil temperatures. Plants have better root formation, fewer root diseases and soil-pest problems and require less fertilizer when mycorrhizae are around.” 

They also need less water. The filaments the fungi sends out have the ability to take up moisture from much deeper in the soil, beyond the reach of the plant’s roots. The fungi itself doesn’t need much water, but its filaments will continue seeking it for the sake of the plants, enabling them to survive in situations that would otherwise kill them.

The filaments have another important function, particularly critical in erosion-control applications. Think of them as thousands of tiny fingers holding the soil particles together, thus reducing the potential for further erosion.

Mycorrhizae are even more vital when hydroseeding over mine tailings or other former industrial sites. “Such operations often leave behind land contaminated with high levels of heavy metals, including nickel, zinc, lead, aluminum, iron and cadmium,” said Hreno. “These heavy metals may affect soil pH as well as nutrient cycling and mobility.”

As a result, revegetation may be much less successful, leading to patches of bare, erodible soil. Sediment laden with heavy metals then has a high potential of migrating to and polluting nearby bodies of water. 

Of course, one of the reasons for revegetating such sites is that certain kinds of plants remove heavy metals from soil. Plants symbiotically linked to mycorrhizae can tolerate even higher levels of heavy metals than plants without such linkage. “The mycorrhizae’s fungal sheaths have the ability to store and immobilize heavy metals,” Hreno explained. This prevents the seeds and plants from being poisoned by the toxic metals, and multiplies the effectiveness of the reclamation effort.

“Soils left behind in the aftermath of mining or heavy industrial operations are often also deficient in phosphorus and nitrogen. Since mycorrhizae enhance nutrient cycling and uptake, the plants are better able to take advantage of what nutrients are still present in the soil,” Hreno states.

Mycorrhizae can even help reduce the overall cost of site reclamation and restoration. As you know, that’s an expensive, multistep process, involving the removal of contaminated waste material from the site, restoring and reshaping slopes, adding fertilizers and soil amendments, and finally, reseeding or replanting.  The tab adds up fast.

Even after all of these efforts, if mycorrhizae aren’t present in the soil in sufficient amounts, the new vegetation may fail to establish. Adding mycorrhizae to the soil is cheap insurance against failure.

Topsoil that’s been disturbed by construction just isn’t the same afterwards. Among other things, its natural mycorrhizal content will be significantly diminished. “If those fungi aren’t replaced, it’ll be more difficult for vegetation to reestablish itself on that site,” Hreno said.

Some reclaimed and reused topsoil is biologically active enough to provide sufficient mycorrhizal content. If good topsoil is present on a site before construction begins, it can be preserved by removing it and stockpiling it somewhere nearby.

However, “stockpiling is often done incorrectly, with soil piled up in tall, vertical rows and left alone time,” said Hreno. “Only the very upper levels of the piles remain biologically active. The remaining 80 percent of the soil is dead.” New topsoil can be hauled in, but that’s usually very expensive.

“If they pulled soil out of the subsurface from ten feet down,  brought that up to the top, and that became the topsoil, you’d probably have some mycorrhizal issues,” said Richmond. 

A cheaper solution is to bring the existing topsoil back to life by adding soil amendments that can replace the missing mycorrhizae. Verdyol Biotic Earth and Holganix are two examples, but there are many others.

“Verdyol Biotic Earth incorporates sustainably harvested sphagnum peat moss as its main organic component,” said Hreno. “The sphagnum moss is supplemented with straw, flax fibers, and precise amounts of mycorrhizae, selected because they work well with sphagnum peat moss.”

“Holganix contains 20 different species of both ecto- and endomycorrhizae,” said Neidermyer.  “That pretty much covers all the different types of plants that would be used in hydroseeding applications. There are separate formulations depending on what mixture of grasses and/or wild seeds you’re using.”

Robert Arello, owner and president of Hydrograss Technologies, Inc., of North Oxford Massachusetts and Sarasota, Florida, doesn’t think adding mycorrhizae alone is the answer.

“We’ll use combinations of mycorrhizae with other things, like humic acid, either in a dry or liquid state,” he said. “We also use Sustain’s organic turkey manure, and Bioprime, a product that has a combination of slow-release fertilizers and a plant growth promoter that softens seed coats.” (Some mycorrhizae supplements already contain humic acid.)

Barrett Ersek, founder and CEO of Holganix, warns against adding too much humic acid, especially in a very concentrated form.  It could cause a burn. As for mycorrhizae, however, “you can’t possibly put too much down. It won’t hurt anything.”

However, he does say that when you’re talking about adding biostimulants like Holganix, you’ve got think about everything else you’re putting in the tank, specifically, fertilizer.  Remember that you’re greatly increasing the efficiency in which those plants uptake the N, P and K. 

“If you’ve put down too much fertilizer and then add a biostimulant, you’ll accelerate that burning effect, because you’ve just turbocharged it,” Ersek cautions. “And there are some other chemical additives that get enhanced with biostimulants that can also add burn potential.”

If you’ve never added a biostimulant product to your hydroseeding mix before, Ersek advises cutting the fertilizer back by 50 percent. Some of his hydroseeding contractor customers with more experience using such products cut their fertilizer rates back even further.

Arello says that with denser, more claylike soils, hydromulching alone may not be adequate. “We had that problem with one particular site. We actually punched holes into the dirt, scarified it so we could really work that mycorrhizae down in there.”

Ersek says it doesn’t matter whether you use jet or mechanical agitation, either. Yes, mycorrhizae are living organisms, and some may be beaten up or even killed by paddle agitation, but the collateral damage is so tiny that’s not really a concern. As far as killing mycorrhizae goes, Arello says sites with salty well water are much more likely to commit mycorrhizae-cide.

Amendments like these can be added directly to hydroseeding mixes and applied to sites even where there is little or no topsoil present. 

Or water. When hydroseeding, you’re usually not applying any additional water, other than that used to make the slurry itself. You can see how the fungi’s water-seeking ability is a big plus here. “If you’re hydroseeding in a drought-stricken area, or one where irrigation is either not allowed or not available, the addition of mycorrhizae could be the single biggest factor in the success of that project,” stated Hreno.

We’ve spent a lot of time talking about mycorrhizae, but we shouldn’t close before mentioning the importance of soil bacteria. “It’s the bacteria that promote early germination,” said Neidermyer.

“As soon as a seed germinates, the very first thing that gets going is its roots. The mycorrhizae associate with the roots, and that’s important, because you need to bring water and nutrients to the newly germinated, emerging plant so it can thrive.”

Soil amendments containing mycorrhizae help vegetation not merely get established, but off to a great, healthy start. Adding mycorrhizae to a hydroseeding mix will help the seeds derive maximum benefit from the fertilizer that was applied along with them. And, it can do it using less water, and at less than half the cost of hauling in brand new topsoil from far away. 

Why not fix the soil that’s already there?

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