Mycorrhizae: Beneficial Fungi in Fertile Soil

 

Mycorrhizal fungi form a symbiotic association with the roots of most plants. The fungi grow into or between the cells of the roots and use ten percent of the carbohydrates the plant passes from the leaves to the roots. The fungi do not have chlorophyll in the presence of sunlight, so they can't manufacture carbohydrates. In return for the energy taken from the plants, the fungi grow out and search far and wide for nutrients and moisture. They feed the plant so it can continue to manufacture more and more carbohydrate energy. A plant well colonized with mycorrhizal fungi will have the equivalent of ten times more roots than one without the fungi.

 

Another benefit of this association is that, as long as the fungi is flourishing, it can prevent all root pathogens and damaging nematodes from attacking the plant root.

 

Decaying organic mulch on the soil keeps both the plant and the many beneficial soil species, such as the mycorrhizal fungi, flourishing so they can help each other.

 

The appearance of mycorrhizal fungi was reported in 1885 by a German botanist, A. B. Frank, who believed that water and soil nutrients might be entering trees through these fungi. This fungus acts as a link between the soil and rootlets of the plant. It flourishes in humus. When the association is present, plants are strikingly vigorous, achieve good growth, and gain resistance against attacks by insects and diseases.

 

Among forest trees and other plants, including food crops, the mycorrhizal association is widespread, habitual, and at times essential. It is stimulated when there is ample light, adequate pH of the soil, good aeration, humus, and moderate soil fertility. It is inhibited by the presence of many chemical fertilizers.

 

It has been found that these fungi can play an important role in plants grown in infertile soils where phosphorus, zinc, and copper are especially scarce. Mycorrhizae assist tree growth in such soils. As the plants prosper, so do the fungi, since they depend on food from the plants for their own energy. They use about 10% of the carbohydrates transported from plant leaves to the roots.

The efficient system works as follows: As plant roots grow, they encounter zygomycetes, a family of soil fungi. These fungi enter the roots through root hair or root epidermal cells, and grow in the soil. They form hyphae, a network of tiny, thread-like tubes. The hyphae seek out nutrients that are poorly available in the soil areas unexplored by the roots. Hence, the root system is extended by the fungi, since the hyphae enable the plant to explore more areas and to obtain more essential nutrients in useable solution forms than could be possible otherwise.

Within the root, the fungus forms two different structures: vesicles and arbuscles. The former are round, balloon-like structures that store carbohydrates from the roots. The latter are highly branched structures that accumulate nutrients, absorbed by the hyphae, that can be released to the plant.

 

In studies at Ohio's Agricultural Research and Development Center, it has been learned that the more fertile the soil, the less need there is for mycorrhizae. Also, it has been found that certain fungi perform nutrient-uptake function better than others. By inoculating apple seedlings with an effective mycorrhizal fungi before planting, growth is stimulated.

 

The practical beneficial effects of mycorrhizae have been demonstrated convincingly in different parts of the world. Attempts to reforest areas, which failed because of a lack of mycorrhizal fungi, became successful after the soil was inoculated with pure cultures of mycorrhizae-producing fungi or with soils taken from an old forest stand. In the U.S.S.R., for example, certain steppes have been re-forested with oak, after it was found that seedlings inoculated with mycorrhizal fungi were able to resist the extreme climatic conditions. Similarly, high mountain regions of Austria were successfully reforested with spruce by means of mycorrhizae.

 

In the United States, experiments of prairie soil inoculation produced beneficial effects on poplar cuttings, with better growth and higher survival rate. White pine seedlings cultivated in inoculated prairie soil contained 86% more nitrogen, 230% more phosphorus, and 75% more potassium than plants in untreated soil. It has been demonstrated that mycorrhizal associations unlock food elements from the soil. In experiments, pine seedlings with the fungus had four times as much phosphorus as pine seedlings without it.

 

Mycorrhizal association is of prime importance in tree nurseries and plantation practices. But it is also important to a variety of other plants too, including many cultivated food crops such as cereal grasses, legumes, fruit trees, and berries.

The Garden-Ville Method - Lessons in Nature