A Plant Evolution Revolution Mycorrhizal Fungi Expand Contemporary Cropping Opportunities by Mike Amaranthus, Ph.D. & Larry Simpson

Soil biology has emerged over the last decade as a critical part of the knowledge base for successful and sus- tainable agricultural production. A key component of biology is the profound plant/mycorrhizal fungi relationship, which has enormous potential for im- proved management of contemporary farming systems. Although using these fungi has the potential to revolutionize agriculture they are certainly not new in terms of the evolution of plants.

Where we’ve been The fossil evidence indicates that the specialized “mycorrhiza” (meaning “fungus-root”) plant relationship dates back over 460 million years and actu- ally played a key role in allowing plants to utilize terrestrial habitats. Without mycorrhizal fungi, today’s crop plants A healthy mycorrhizal-inoculated organic winter wheat field in Canada. might not exist, unless you are farming seaweed! For the first 75 million years that plants colonized dry Since before World War II, scientific and technological advances land, they did not have differentiated root tissue and depended in agronomy have focused primarily on the development of entirely on this symbiotic relationship with mycorrhizal fungi to chemical and mechanical approaches to improving crop produc- access nutrients and moisture from the various and often harsh tion yields. Nutrient needs have been addressed using synthetic terrestrial environments. The root structures of plants actually fertilizers while weed suppression has been accomplished through evolved specifically as specialized attachment sites to better ac- tillage and herbicides and plant diseases controlled using an array commodate these fungi and the efficiencies available through of chemical pesticides. More recently, modern science has begun the symbiotic “trading” of water and nutrients for sugars pro- to understand that in natural habitat plant roots are a complex duced by photosynthesis. mixture of both fungi and plant that is fundamental to life on the In this symbiosis, the plant is provided better access to and planet. The vast majority of crops form an association with these uptake of nutrients and water from the soil. In return, the specialized mycorrhizal soil fungi in order to maximize perfor- fungus, which cannot synthesize its own nourishment, receives mance. Among the few but notable exceptions are members of its energy source in the form of carbohydrates donated by the the Brassicaceae plant family (cabbage, broccoli, cauliflower, rad- plant. This highly successful system continues in 90 percent of ish, turnips, canola, etc.) the Amaranthaceae plant family (beets, plant species today. spinach, chard, etc.) and the Polygonaceae plant family (rhubarb, Agricultural science has only in the last decade begun to recog- buckwheat). Virtually all other crop plants worldwide are meant nize the importance of mycorrhizal fungi in farming ecosystems. to host some form of mycorrhizal association.

Reprinted from April 2011 • Vol. 41, No. 4 What ARE cies. Nearly all of the AM fungal species able to penetrate the tiniest pores and Mycorrhizal Fungi? are generalists which will associate with fissures in the soil. The body of the mycorrhizal fun- a wide variety of plants, in a broad as- Research confirms that mycorrhizae gus consists of microscopic filaments sortment of soil types, geologies, topog- are particularly important in mobiliz- called hyphae. Individual hyphae are raphies and climates. ing phosphorus, nitrogen, zinc, iron, approximately 1/25th the diameter of a The numbers of hyphae on a root sys- calcium, magnesium, manganese, sul- human hair and can grow up to 15 to tem can be prodigious. Just a teaspoon fur and other important soil nutrients 25 inches in length. These strands grow of healthy soil can contain up to several by enzymatic release from tightly held from within and around the root cells miles of fungal hyphae. The resulting chemical bonds and transporting them of the host plant, spreading out into the nutrient and water uptake efficiency of back to the plant. Crop plant uptake and surrounding soil, greatly increasing the crop plants is increased considerably. utilization of fertilizer inputs likewise surface area of the root system. The most Agricultural soil often contains abun- becomes far more efficient, often leading widespread type of mycorrhizal relation- dant “pools” of nutrients but the avail- to significant savings in fertilizer costs. ships are known as arbuscular mycorrhi- ability of these nutrients to the crops But mycorrhizal benefits do not stop zae (also commonly referred to as “AM,” themselves may be limited. there. These fungi also play a definitive “VAM” or “endo mycorrhizae”). As stat- role in a plant’s natural defense against ed above, most agricultural plants, in- What they do fungal root diseases such as Pytophthora, cluding most grains, vegetables, orchard This plant-fungus association can de- Fusarium, Phythium and Rhizoctonia. trees, vines and turfgrasses evolved with, liver considerable benefits in agricultural Mycorrhizal fungi produce and release and are naturally “designed” to achieve operations. The effect on the root system suppressive exudates such as antibiotics optimum growth and vigor by forming of a mycorrhizal-colonized plant is ex- that inhibit infection by these and other these fungal relationships. There are ap- tensive. As part of this relationship, most fungal root pathogens. Studies have doc- proximately 150 arbuscular mycorrhizal of the absorbing area of the root system umented that mycorrhizae also defend (AM) fungal species on the whole planet is actually fungal hyphae. Hyphae are far root systems by forming a physical bar- forming with perhaps 300,000 plant spe- thinner than roots or root hairs and are rier to deter invasion by soil pathogens.

Without Mycorrhizae With Mycorrhizae

unavailable phosphorus unavailable phosphorus

available phosphorus

Drawing of AM fungal hyphae (left) without and (right) with mycorrhizal filament accessing pools of phosphorus in the soil.

Mycorrhizal Fungi • Mycorrhizal fungi colonize the plant’s root system and develop a symbiotic association called a “mycorrhiza.” • Form a network of filaments that associate with plant roots and draw nutrients and water from the soil that the root system would not be able to access otherwise. • Mycorrhizae can form on more than 90 percent of crop species. • Certain cropping practices reduce or eliminate mycorrhizal fungi.

Arbuscular mycorrhizal (AM) fungal hyphae.

Reprinted from April 2011 • Vol. 41, No. 4 Mycorrhizae Advantages

• Allows plants to draw more nutrients and water from the soil, including nitrogen and phosphorus • Results in vigorous and healthy plants • Better yields • Protects roots • Increases tolerance of drought and others stresses • Enhances flowering and fruiting • Reduces nutrient loss • Reduces weed competition Diagram of thin mycorrhizal filaments accessing nutrients.

during periods of drought. Plant systems in natural areas generally achieve levels of drought tolerance far exceeding those found in agriculture partly due to the enormous web of mycorrhizal hyphae which act like a giant sponge to protect the plant communities from extreme soil moisture deficits. Mycorrhizal filaments can penetrate into the smallest of soil pores and fis- sures to access microscopic sources of water that are unavailable to the thicker roots. An extensive body of research documents the importance of the my- corrhizal relationship for efficient water use and drought protection among a wide array of important crop species. The declining availability of water and its ever-increasing cost are formidable Drought stressed conventional, non-mycorrhizal corn wilt (right) compared to organi- issues facing today’s farmer and mycor- cally grown corn (left) at the Rodale Institute. rhizal fungi can be powerful tools to enhance water-use efficiencies. This barrier is made of “chitin” (the abundant, lush vegetation in natural and Monitoring various crops indicates same tough material that is in mammal wild systems without the benefit of ir- that mycorrhizal inoculation is having claws and insect shells) which forms a rigation. How do natural areas provide a positive effect on yields. For example, tough, protective layer over the outside for such luxuriant plant growth without data presented at the 2010 National Al- of root cells. irrigation? lium Research Conference in Sparks, Ne- One key factor is the mycorrhizal vada showed onion seed treated with a Drought tolerance & yield threads attached to plant roots, which powdered endo-mycorrhizal (4-species) No one understands better than so thoroughly scour the soil for available product outperformed controls. Average farmers that agriculture’s need for fresh resources. They absorb water during yields on the mycorrhizal-treated onions water is not always in sync with nature’s periods of adequate soil moisture, then were 62 percent greater compared to con- inclination to provide it. We often see retain and slowly release it to the plant trols and significantly greater than any

Reprinted from April 2011 • Vol. 41, No. 4 other treatments. At this rate of increased losses were reduced 30 percent with my- biomass of sunflower grown alone in production, the return to the grower (at corrhizal inoculation. monocultures was 22 percent higher $10 per 50 pound bag and an extra 600 In other recent research (van der compared to microcosms where sun- bags acre) would be $6,000 per acre on Heiden et al. 2010,) AM fungi-inocu- flower was grown in mixture together a $20 per acre investment in mycorrhizal lated soils lost 60 percent less phospho- with weeds,” while “the total weed bio- inoculum. Recent harvest results of a rus and 7.5 percent less ammonium mass in microcosms with sunflower was rice trial in side by side 75-acre blocks in compared to control areas without AM on average 47 percent lower in micro- California’s Sacramento Valley yielded fungi. Similar results were obtained for cosms with AM fungi, compared to mi- 8 percent more grain in the MycoApply areas planted with each of three different crocosms without AM fungi.” And when inoculated seed area compared to the plant species. In research by Rinaudo et the weeds were grown alone, the effect of control area — an extra $173 per acre al. 2010, the authors note that “previous AM fungi presence was to reduce weed and a 10-fold return over the cost of the work has emphasized that AM fungi biomass by 25 percent. mycorrhizal inoculum. In another 2010 California study, Barley seed inoculated with a powdered, 4-species endo-mycor- rhizal product resulted in average yields of 7,778 pounds per acre compared to 6,030 pounds per acre in control areas — a 29 percent increase. The mycorrhizal- inoculated barley was at least 6 inches taller than the untreated crop and netted an extra $145 per acre. In Wisconsin at Gagas Farms, Inc., soybeans were inocu- lated with a liquid mycorrhizal inoculant. Yield was significantly increased by over 9 percent compared to side-by-side, non- treated areas.

Conserving Nutrient Capital Nutrient loss from agricultural eco- systems is among the top environmental Example of MycoApply Mycorrhizal inoculated onions at left compared to controls on threats to ecosystems worldwide, lead- right. ing to reduced plant productivity on the farm and eutrophication of surface are important for the sustainability of What it means water near nutrient-rich ecosystems. agricultural ecosystems by enhancing Rinaudo et al. say their study shows Hence, it is of pivotal importance to crop nutrition by providing protection that “AM fungi have the ability to sup- understand AM fungi, whose absorbing against stress and disease and by improv- press the growth of some aggressive agri- filaments are widespread across nearly ing soil structure.” cultural weeds, including Chenopodium all natural ecosystems and reduce nutri- album and Echinochloa crus-galli, which ent loss from irrigation or rain-induced Weed suppression belong to the top ten of the world’s leaching events. In their new study, Rinaudo et al. most aggressive weeds.” In addition, Corkidi, et al. 2010 at the University 2010, explore another positive impact of they note that the sunflower plants they of California, Riverside and Internation- AM fungi: the ability to suppress nega- grew “benefited from AM fungi through al Plant Propagators Society found that tive consequences of aggressive agricul- improved phosphorus uptake,” which mycorrhizal plants grown in half and tural weeds. It has been estimated that “points to a novel characteristic of the full rate of fertilizer were significantly annual crop yields around the world are mycorrhizal symbiosis, namely that AM larger than non-mycorrhizal plants. The reduced 10 to 30 percent. fungi have the ability to suppress un- authors also found that shoots from wanted weed species, while at the same mycorrhizal plants averaged 30 percent What was done & learned time promoting nutrition of the target higher nitrogen content and a whopping Rinaudo et al. write that they “in- crop species.” They note that their find- 300 percent higher phosphorus content vestigated the impact of AM fungi and ings “supports two earlier reports by Va- than shoots of non-mycorrhizal plants. AM fungi diversity (three versus one tovec et al. (2005) and Jordan and Huerd Perhaps more importantly, the authors AM fungal species) on weed growth in (2008).” And in further comments, they documented a significant reduction in experimental microcosms where a crop state that “sunflower obtained 48 per- the nitrates, ammonium and phosphate (sunflower) was grown together with cent more phosphorus when AM fungi found in leachates for the full rate of six widespread weed species.” The four were present, while fungi reduced weed fertilization. Ammonium and phosphate researchers go on to state that: “the total phosphorus content of the three non-

Reprinted from April 2011 • Vol. 41, No. 4 mycorrhizal weeds (Digitaria sanguina- survive for any extended duration with- Living soil lis, Echinochloa crus-galli, Setaria viridis) out the presence of living roots. From the food we eat, to the air we by 21 percent.” 2. Tilling, which by itself may adverse- breathe, to the clothes we wear, humans ly affect mycorrhizae, generally leads to depend upon the thin covering of the Does My Farmland fallow conditions, which in turn, impacts Earth’s surface we call soil. Arguably Have Mycorrhizae? the fungi. Therefore, even no-till prac- this thin and fragile layer of living top- Certain modern agricultural practices tices may not necessarily preserve my- soil is the Earth’s most critical natural are known to suppress biological activity corrhizae either. When annual crops are resource. Lately there has been tremen- in soils. Land clearing, fungicides, certain harvested, the roots soon die and any my- dous interest from farmers about using chemical fertilizers, cultivation, compac- corrhizal fungi die with them unless new soil biology, the evolutionary revolution tion, isolation from natural area, soil living roots are introduced in the form of that brought plants to land 460 million erosion, organic matter loss and periods another crop within several weeks. One years ago, to increase crop yields while of fallow are all factors that can contrib- might think that the spores left in the protecting and improving our valuable ute adversely to populations of beneficial soil would regenerate the mycorrhizal soil resource. mycorrhizal fungi. Soil testing worldwide populations in the next crops planted The predicted increase in world pop- indicates that many intensively managed even after an absence of living roots and ulation and the inevitable global surge crop and pastures lack adequate popula- hyphae. However, for annual crops, few in demand for food, feedstocks and bio- tions of mycorrhizal fungi. if any spores develop in one year and fuels will require a shift toward more Basically, loss of naturally occurring after repeated cycles that include regular sustainable, biological farming methods. mycorrhizal fungi comes about in three intervals of fallow, those few spores that Worldwide fertilizer and herbicide costs fundamental ways: are present eventually expire and are not have already increased dramatically over 1. Fallow soil is among the biggest sufficiently replaced by the gradually di- the past five years and farmers may be causes for the demise of mycorrhizal minishing mycorrhizal populations. finding themselves relying less on syn- fungi. The fungi are dependent on their 3. The other critical situation that thetic chemicals to grow crops. Mycor- host plants for sustenance and cannot eventually eliminates mycorrhizal popu- rhizal inoculation offers a great solution lations from many agricultural lands is to a more efficient use of fertilizers and lack of proximity to natural populations as a weed suppressant. More and more from which new colonization usually growers are finding that they can reduce spreads. The crop plants become isolated their fertilizer and water costs up to 30 from the beneficial mycorrhizal fungi percent while increasing yields by inocu- that would, in natural ecosystems, be lating with mycorrhizal inoculum, an Acres U.S.A. is the national journal of abundantly available to spread coloniza- evolutionary success story that is starting sustainable agriculture, standing virtually tion to their roots. Without adjacency a revolution in our thinking today. alone with a real track record — over 35 years of continuous publication. Eash to natural areas acting as a source of mycorrhizal hyphae and spores to re- Dr. Mike Amaranthus has been working issue is packed full of information eco- with mycorrhizae for 34 years as a USDA re- consultants regularly charge top dollar populate depleted lands, arbuscular my- search soil scientist, adjunct associate univer- for. You’ll be kept up-to-date on all of corrhizal populations are very slow to sity professor, and lead scientist for Mycorrhizal the news that affects agriculture — regu- Applications, Inc. He has published over 80 lations, discoveries, research updates, re-establish. Arbuscular mycorrhizal fungi pro- research papers on the use of mycorrhizal fungi organic certification issues, and more. and been featured on several national and duce their spores below ground and do To subscribe, call international television specials. Tools, articles, not move readily via wind or water, but pictures and video using mycorrhizal inoculum 1-800-355-5313 rather grow from root to root. Therefore are available at www.mycorrhizae.com. (toll-free in the U.S. & Canada) re-colonization across long distances Larry Simpson is director of education and 512-892-4400 / fax 512-892-4448 back into farm soil from undisturbed training at Mycorrhizal Applications, Inc. Grants P.O. Box 91299 / Austin, TX 78709 natural sites becomes slow and difficult. Pass, Oregon. Larry has travelled extensively [email protected] Unfortunately, growing crops immedi- communicating ways to practically use mycor- ately adjacent to undisturbed natural rhizal inoculant to achieve the greatest gains Or subscribe online at: for end users. Contact him via e-mail at larry@ ecosystems is not always an option in www.acresusa.com mycorrhizae.com. modern agriculture.

Reprinted from April 2011 • Vol. 41, No. 4