Mycorrhiza

As mycorrhizal ( altgr. μύκης mykes, mushroom ' and ῥίζα rhiza, root '; majority mycorrhizae or mycorrhizas ) is defined as a form of symbiosis between fungi and plants in which a fungus is with the fine root system of a plant in touch.

Basics

The mycorrhizal fungi provide the plant nutrient salts and water, and in turn receive a portion of assimilates produced by photosynthesis ( green ) plants. The proportion of primary production, is transferred to the fungus can be up to 25%. Unlike other soil fungi mycorrhizal many missing enzymes, which would be needed to break down complex carbohydrates. Therefore, these are dependent on the supply by the plant. The mycorrhizal fungi have a significantly larger compared to plant assets, minerals and water to remove from the soil. Often the water, nitrogen and phosphate supply of the " infected " plants is improved, continues to offer the mycorrhization some protection against root pathogens and generally increased the drought resistance of plants, which may be mainly due to extreme locations of advantage.

Because of their ability to deliver nutrients directly to the roots of crops, is now investigated whether it is possible to use mushrooms as a substitute for mineral fertilizers. The static range for the global fertilizer stocks is only 50 to 100 years. Mycorrhizae may form an alternative.

For optimum growth, many plant species are dependent on specific mycorrhizal fungi. From an evolutionary perspective, however, is largely unclear why the Mykorrhizapartner should always occur as Mutualist. Symbioses are generally vulnerable to exploiters and deceiver, because it is always more cost effective for the deceptive partners, reap the benefits of the partnership to deliver (eg, easily digestible nutrients of the plant), without a quid pro quo (eg minerals). Therefore, recent concepts in the mycorrhizal plant symbiosis expect a gradient of relationships, ranging from mutualism to parasitism strict. Plants also try to benefit from mycorrhizal fungi, without providing any services in return. Mycorrhizal plant parasites can be found at orchids ( eg Korallenwurz and Neottia ) and chlorophyll-free parasitic plants (eg Corsia ). Research into the mechanisms of mutual manipulation and deception between symbiotic partners is a research field of modern ecology.

The symbiosis of land plants with fungi occurred already in Devon, so to 400 million years ago. Of the land plants about 90 % are capable of Mykorrhizabildung, with about 6000 species of fungi can socialize with plants located. It is believed that the arbuscular mycorrhizal (AM) in the first enabled state colonization by the first terrestrial plants. Globally, around 200 species of VA mycorrhizal fungi - (see below) described that are in symbiosis with about 80 % of all land plant species. Such non-specific symbiosis may have evolved subsequently difficult. Begon, Harper and Townsend write in their textbook of Ecology ( 1986) even: "Most higher plants have no roots, they have mycorrhizae. " ( In engl Original:. "Most higher plants do not have roots, theyhave mycorrhizae. " ) The quotation is taken from the American plant pathologist Stephen William and reads in the original: ". ... in agricultural field conditions, plants do not, strictly speaking, have roots, theyhave mycorrhizas "

Classification

Due to specific characteristics of the mycorrhizae are traditionally divided into three different groups. Another classification distinguishes between five mutualistic (ecto -, endo- ECT, arbutoider, ericoider and VA ) and two antagonistic ( orchids and monotropoider ) mycorrhizae (after Smith & Read 1997, modified).

Common to all forms that fungal hyphae permeate the soil and transport nutrients to the plants.

Ectomycorrhizal

This link provides the highest in Central European forests most common root symbiosis Represents the mycelium ( totality of branching hyphae ) forms a tight jacket ( sheath) around the young, unverkorkten root ends. In response, the root ends swell clavate and develop no root hairs. The fungal hyphae grow in the root bark into it, but do not penetrate root cells but form in the Extrazellularräumen a network that the nutrient exchange between fungus and plant facilitates ( HARTIG network). The hyphae of the fungus take over the task of the lack of root hairs. They extend far into the soil matrix into it, so good, and extensive nutrient and water absorption is ensured. In addition, the mycorrhiza protect tree roots from infection by the intrusion of other bacteria or fungi. This type of mycorrhiza is typical of trees from the families of birch, beech, pine, willow and rose plants. Fungal partners are mostly stand mushrooms from the orders Agaricales Boletales and, in rare cases, Ascomycota such as truffles and special mug warmers like the cedar sand bristle Ling. While most plants Partner at suitable locations also can thrive without fungi, there are some among them who are obligately dependent on fungi as a partner. It is believed that a great many large fungi for ectomycorrhizal are capable - in Central Europe over 1,000 species from the genera veil compacts russulas and Milkcaps, Knight Linge, Linge Schneck, and amanita amanita mushrooms, chanterelles.

Endomycorrhiza

Here penetrates a part of the hyphae of the fungus into the cells of the root cortex of plants partner. The latter are mostly herbaceous plants, rarely trees. The network of hyphens that surrounds the root in the ectomycorrhizal missing here. Within the cell, the fungi form a kind of haustorium. This allows nutrients and water, whilst carbohydrates are added. Plant species of the following families are almost always with a fungal partner in symbiosis: Heather, wintergreen plants and orchids. The symbiotic mushrooms are mostly stand fungi from the order Tulasnellales, and their anamorphic forms Rhizoctonia and Orcheomyces. At least with this type of orchid endomycorrhizal is required for their development.

Arbuscular mycorrhiza

Arbuscular or vesicular- arbuscular mycorrhizal outdated and is a special form of Endomycorrhiza: typical of this common type of mycorrhizae are the formation of arbuscules - these are branched, delicate hyphae in tree form within the root cells. Some taxa also form vesicles - in the root tissue of the plant to form thick-walled fungal cells. The number of plants which may benefit from the AT is very large. Many of these are crops whose increased by the symbiosis phosphate supply can have a positive effect on the yield. The fungi involved assigns you the arbuscular mycorrhizal fungi in the newly created Division ( phylum ) Glomeromycota to.

History

The discovery of mycorrhiza was a multistep process. In the years 1840-1880 several individual observations that had to do with the phenomenon appeared. Only Franz Kamieński (1881 ) and Albert Bernhard Frank (1885 ) identified the overall picture correctly and published works with clearly running experiments. The word mycorrhiza was first used by Frank.

Today, there are several European countries systematic collections of mycorrhiza. One of them operates the Agricultural Research Station Agroscope in Zurich, where already half of the known 100 in Switzerland mycorrhizal fungus ball types are represented. They grow in pots filled with oil binding agent. The porous granules is in the moist state a base substrate to obtain the fungi alive. Based on such collections, the researchers can examine the specifics of their properties. Goal is to determine, among other things, with which plants form a nutrient which fungal species network. This knowledge could be of organic farming, weed control or the Greening of flat roofs of use.