**2. Ecology of mycorrhiza**

The mycorrhizal fungi are distinguished by their living in different environments, including tropical rainforest and sandy desert ones. Many factors affect the spread of mycorrhizal, as well as the processes of sporulation formation, and the way they coexist with mycoflora or other soil revivals, root colonization, colonization formation. We find ourselves in an urgent need to understand these stages of the presence of fungi as we approach the practical aspect of these fungi. Therefore, it is customary to express the presence of fungi with a term called dispersal. While concerning this process to such fungi, studies indicated that they were present in different continents before the flood and drought process occurred. As for the important study in mycorrhiza, the plant fossils proved that they contain a type of fungi and consist of structures similar to some extent to the mycorrhizal structures (vesicular—dendritic), which he led the researchers to say that these organisms were formed on the roots of forest plants and some natural plants. According to this, what Frank [1] made of his diagnosis of mycorrhizal fungi is a reality and a fact, but it did not attract the attention of scholars in that period or era.

#### **2.1 Means of spreading mycorrhiza**

Several ways to spread it have been suggested:

#### *2.1.1 Active dissemination*

It can appear from one area to another as a result of the growth of hyphae. It was found that the rate of mycorrhizal spread varies according to the density of these soils with these fungi, as well as the plant host that coexists with it. It has been proven that the rate of spread of these fungi reaches within 65 m per 150 years, which means 0.43 m/year, and it was clarified that the soils containing these fungi have a higher prevalence rate than the soils that do not contain these fungi. The type of plant and root density plays an important role in the spread of mycorrhizae. It was mentioned that the soils planted with subclover pasture plant in Australia have the prevalence of mycorrhizal *Glomus fasciculatum* up to 1 cm per week, but in another field when the vegetation cover prevails in it when one of the weeds was found. The spread of this type of mycorrhiza decreases and reaches about 0.07 cm, and from this we can show that the density of roots plays a key role in determining the spread of mycorrhizae, especially in the young stages of plant growth, where we find that the vegetation cover of weeds had a low prevalence rate, but the prevalence rate increased by changing the second type to clover because there is a wide difference in the root system of both plant hosts.

Poter [2] worked on the distribution of mycorrhizae with the type of soil when he took the mycorrhizal vaccines and added them to soil A. He noticed that the growth of hyphae as well as the infection and formation of spores differed significantly with other soil B, and at that time he attributed the reason to that there is a possibility that soil A in it encourages factors for the growth and formation of spores of this fungus compared to soil B, then he started transferring samples of mycorrhizae to soil C and noticed a strange observation than this, which is that mycorrhizae cause infection but do not form spores. As for soil B, after taking the inoculum from it and transferring it to soil C, the mycorrhizal system lost the ability to form spores, but it kept the infection, and it was found that there are three factors affecting the distribution of mycorrhizae in the soil, namely:

