As bonsai enthusiasts we’ve all heard about mycorrizha, which is supposed to be beneficial to the root system of our bonsai.
Is there any truth in this claim or is it just another commercial hoax?
Text: Tristan Linden – Photographs: Servaplant
The name mycorrhiza originates from the Greek words mykos and rhiza meaning fungus and root respectively. The name mycorrhiza does not refer to the fungus. The mycorrhiza (plural mycorrhizae) is the symbiotic relationship between the plant’s roots and one or more fungi. This symbiotic relationship occurs in about 90% of all plants globally. When taking a stroll through a forest we can recognise a lot of these fungi: many mushrooms are the carpophores, the fruiting bodies of fungi. You may have seen the penny bun (boletus edulis), the chantarelle and the fly agaric on your stroll and you probably saw them close to a tree or shrub. To be exact, the fruiting body of a fungus is in a symbiotic relationship with the root system of a tree: a mycorrhiza.
Back in time
Mycorrhiza forming fungi are old, very old; older even than all plants that occupy our planet. They are probably 500 million years or more. Fossil remains from the Devonian period clearly show traces of mycorrhiza. When plants started to invade the land they used photosynthesis as an energy source, but their root system wasn’t yet evolved enough to find and easily absorb all necessary nutritious substances and water. The fungi on the other hand were perfectly adapted to the soil, but depended on higher plants for their source of carbohydrates. They complement one another perfectly: what one cannot do the other can.
The fungi’s characteristics
Mycorrhiza fungi form the link between the plant and the soil. Part of the fungi tissue grows into and around the root and in this way it enlarges the absorption area of the plant. Another part, the fungus filaments we can see in the soil (especially with a magnifying glass), invade the soil and enlarge the area for absorption for the plant by a few hundred times. These filaments are about three micrometers in diameter and establish vast webbing in the soil. The filaments grow into the smallest pores of the soil and free nutrients for the plant by using enzymes and organic acids. In this way the intake of nutrients by the plant is increased many times, in quantity as well as in quality. The plant can absorb more nutrients, but can reach also those nutrients it normally cannot absorb by itself.
Morphology and development
Under normal conditions, in Nature, mycorrhiza fungi develop within one to three months after the seedling has germinated. The little plant stands close to older congeners (organisms within the same genus) and its roots are colonised by their fungi or by fungi that are transferred by wind or animals. The fungus reacts to minimal amounts of chemical substances the seedling’s roots release. A sheath of fungus is laid around the young roots tips and hyphae, very fine filaments, invade the roots. From there the filaments grow into the soil. They more or less take over the root tip’s role. The first mycorrhiza fungi live for about 1 to 3 years after which their role is partly or totally taken over by fungi that are more adapted to this specific soil or these particular conditions. In this way a mature tree can be host to many different mycorrhizal partners. The Douglas fir for example is known to have more than 2,000 different mycorrhizal partners.
The relationship between the host plant and the fungus is a symbiosis: they give one another substances they cannot obtain for themselves. The mycorrhiza is fully dependent on the host plant for its survival. The host plant will survive without it, but with much more difficulty. The fungus takes full advantage of the relationship: the tree transports sugars to the fungus sheath where they are converted into typical fungus sugars. The fungus holds the sugars in reserve to form fruiting bodies in autumn: mushrooms. About ten per cent of the tree’s nutrients are transported to the fungus. The sheath of the fungus is also storage for spore elements that the fungus — and also the tree — can use in times of active growth or shortages in the soil, for example in times of drought. The symbiosis is beneficial for the tree as well: the root system’s absorption area is many times enlarged. The capacity for absorbing less mobile elements like phosphorus and potassium is enormously increased as well. The tree becomes less susceptible to disease because the fungus competes with bacteria for nutrients and space. By producing phytoalexin the fungus stimulates the tree’s immune system. Along the entire length of fungus filaments substances are discharged that are nutrients for all kinds of beneficial bacteria. These bacteria break down substances and produce others. Many of these substances are absorbed by the filaments and end up as nutrients for the tree. The host plant profits from the microclimate that the fungus produces: the production of soil aggregates and, as a result, a better soil structure. The fungus stimulates a richer soil life, containing more and more varied micro-organisms. And in hard times the tree can fall back on the reserves accumulated by the fungus.
The various types of mycorrhiza fungi
Mycorrhiza fungi can be divided into two different types: Ectomycorrhiza fungi that grow around the roots forming fruiting bodies like mushrooms. These are found particularly in ligneous plants: coniferous trees from the family of Pinacea: European or Norway spruce, silver spruce, Douglas spruce, hemlock spruce, fir, larch and cedar. Deciduous trees from the Fagacea family: beech, oak, chestnut; Tiliacea: large and small-leaved linden; Betulacea: birch, alder, hop hornbeam; Corylacea: white beech, hard beam, and hazel; Salicacea: willow, sallow and osier; poplar, aspen, cottonwood and many others. Nearly all forest eco-systems of the northern hemisphere depend on these mycorrhiza fungi. As far as we now know there are about 6,000 types of ectomycorrhiza fungi. We have to realise that some plants are, or can be, host to many different types of mycorrhiza fungi. At the same time, a particular mycorrhiza fungus can occur with many different trees or plants. Some fungi on the other hand are very much bound to a particular climate or a particular tree.
Below: The coral like structure of Ectomycorrhizae
Endomycorrhiza fungi are the oldest in evolution. The fungus is also called arbuvascular mycorrhiza (AM) or vesicular arbuscular mycorrhiza (VAM). There are probably 150 types globally. These fungi penetrate into the cells of the root cortex where they form the characteristic bean-like little organs for the transfer of sugars and nutrients. From the colonised roots filaments grow into the soil. Here they act as an extension of the root system. The spores of the arbuvascular mycorrhiza fungi are distributed by animals. These fungi do not produce fruiting bodies like mushrooms and one cannot see them with the naked eye; only under a microscope do they become visible. Apart from these there is also the Ericoid mycorrhiza (ERM) which grows with the rhododendron and the orchid mycorrhiza that grows with orchids. A number of plants are known to be host for both endo– and ectomycorhiza fungi.
Mycorrhiza is relevant to agriculture, horticulture and forestry. In the past decade much research has been conducted into mycorrhiza fungi. In Germany, Professor Doctor Ingrid Kottke has been one of the pioneers. In Holland Dr Claudia Külling and Dr Ingrid Weissenhorn are often consulted. Research indicates that newly planted trees in forests grow significantly better when treated with mycorrhiza fungi: there is less die-off and considerably better growth and health of the newly planted trees. In horticulture, experiments are carried out on a large scale. It is now possible to grow mycorrhiza fungi and spores of both ectomycorrhizha and endomycorrhiza are available.
Mycorrhiza and bonsai?
What does all this mean for us bonsai enthusiasts? Will adding mycorrhiza to our soil do any good? Yes, certainly. But mycorrhiza fungi are natural partners of trees and of bonsai as well. Scientific research shows that a plant with its natural mycorrhiza partner will grow better in new soil, will be healthier and less susceptible to disease, drought and pollution. This is also true for your bonsai. A bonsai with mycorrhiza fungi will be more vigorous and will take in nutrients more easily and in larger quantities. Your bonsai tree will be more immune to disease and will grow better. But mycorrhiza fungi are not the elixir of life and won’t turn an average bonsai into a prize winning tree.
However, one has to keep in mind that the chance of over-fertilizing grows. The intake of nutrients becomes easier, so you might want to use organic fertiliser that releases its substances more slowly. And before one starts adding mycorrhiza fungi it might be wise to check whether it’s necessary. Most conifers naturally have ecto-mycorrhiza fungi and when taking the tree from its pot they should be visible: microscopically thin, white, woolly filaments around the hair-roots and all through the pot. Ever seen tiny mushrooms in your bonsai pot? Then you can be reasonably sure that your tree has its mycorrhiza partners with them. When a tree forms a symbiosis with endo-mycorrhiza fungi it is more difficult to judge. A tree styled from nursery garden material will probably have few or no mycorrhiza at all. Imports from a country like China will, in most cases, be without fungi. A yamadori that has some of its original soil added to its new pot every time it’s repotted probably has enough fungi, even when it is fully on Akadama. Mycorrhizae adapt to local circumstances. There is no fear of starting a new pest by adding mycorrhiza fungi to your soil when repotting. If you are doubtful about whether or not to add fungi, you can consult a company like Servaplant in Holland, Rootgrow in the UK, or check out the German website listed below. Servaplant can check root samples and these specialists are able to tell you exactly what state your bonsai is in.
Instructions for use
If you decide to give back to your bonsai its natural partners you might want to order mycorrhiza spores. Companies like Servaplant or Rootgrow sells mycorrhiza for most common conifers and deciduous trees and they can tell you what type your tree needs. The spores come in pellets and have to be added to the hair roots. There are two ways of doing it: next time you repot your bonsai spread some pellets at a number of spots around the hair roots. The other way is to make a dozen small holes in the soil and add the pellets after having dissolved them in water. The spores will germinate and it will take one to three months before your tree starts to profit from its new partners. You might want to take that into account when you start adding spores. The best time is spring, but you can add mycorrhiza in summer as well. The fungi live up to three years, so after that time you may want you repeat the therapy. On a conifer you will probably see the fungi next time you repot your bonsai and you might even see tiny mushrooms. What’s more, you stand a good chance that your bonsai is much more vigorous and healthy.
arbuvascular mycorrhiza (AM) or vesicular arbuscular
For more information : www.servaplant.nl (Dutch, German and English) www.coriza.nl
UK: www.rootgrow.co.uk and www.micorrhizas.info
Germany: www.mycorrhiza.de and www.mycorrhiza-research.de
To sum up
A bonsai with mycorrhiza fungi will be more vigorous and will take in nutrients more easily and in larger quantities. Your bonsai tree will be more immune to disease and will grow better. Especially when repotting or when you work with starter material from a nursery it might be wise to add mycorrhiza to the roots.
Conifers: yew, redwood, Sequoiadendron giganteum, Metasequoia glyptostroboides, Thuja, Cypress, Common Juniper, Chamaecyparis, Podocarpus.
Deciduous trees: maple, elm, hackberry, Zelkova, Fraxinus excelsior (Ash), Ligustrum vulgare (Wild Privet), Ilex aquifolium (Holly), Hibiscus, Forsythia, Euonymus, Mimosa, Buxus, Viburnum, Ficus.
Coniferous trees from the family of Pinacea: European or Norway Spruce, Silver spruce, Douglas spruce, Hemlock spruce, the fir and the Larix and cedar.
Deciduous trees from the Fagacea family: beech, oak, chestnut; Tiliacea: linden; Betulacea: birch, alder, hop, hornbeam; Corylacea: white beech, hard beam, and hazel; Salicacea: willow, sallow, osier; poplar, aspen, and cottonwood and many others.
Apart from these there is also the Ericoid mycorrhiza (ERM) which grows with the Rhododendron and the orchid mycorrhiza that grows with orchids.
Servaplant’s various products; more details on www.symbiom.com