*2.4.1 Soil fertility*

Soil nutrients, especially phosphorous, are one of the most important abiotic factors that affect the mycorrhizal fungi. Both nitrogen and phosphorus significantly affect root colonies when they are present at high levels. Therefore, the state of

balance for these two elements is a required condition, that is, the nutritional needs of the family. The plant and the nutritional needs of the living organism should not be within the critical sufficiency limit because this simply means entering into a kind of competition for the source of food, and this explains that some plants vaccinated with VAM may decrease their dry weight or growth rate because the VAM and the plant are included in this type from the competition so that the rate of net photosynthesis is insufficient for both the VAM and the plant, and thus the interference changes from Mutualism (+, +) to (−, +) Parasitism.

There is some information about the negative effects of nitrogen fertilizers on the formation of mycorrhizae, and it was found that nitrogen (ammonia nitrate) clearly reduces both the infection of mycorrhizae and the number of spores in wheat fields. As plants fertilized with high ratios of ammonium to nitrate have a higher phosphorous content in their tissues than plants fertilized with low ratios of (NH4 + ) to (NO3 <sup>−</sup>), and these high concentrations of phosphorous in plant tissues inhibited infection. The reason for the inhibitory effect of ammonium may be attributed to the low pH in the area rhizosphere and to see the effect of fertilizers on mycorrhizae. The initial fertility of the soil must be known, because in poor soils the production of spores will be limited to the total quantity and not the percentage of infected roots derived from plant growth.

As for phosphate fertilizers, some studies have shown that these fertilizers have negative effects on the internal mycorrhizal fungi. Increasing the processed phosphorous may reduce the infection of mycorrhizae to levels that are insufficient to encourage the absorption of other elements. Phosphorus and zinc of the shoots of pollinated plants grown in low fertility soils were more than that of unpollinated plants. Increasing the level of ready phosphorus is an inhibitor of the growth of mycorrhizal, unlike insoluble forms such as rock phosphate, which is not considered an inhibitor. The results on wheat plants confirmed this, as it was found that the addition of phosphorous levels of 60, 120, and 240 kg phosphorus/ha led to a reduction in the percentage of infected roots in the fertilized treatments compared to the non-fertilized treatments, where the level led to 240 kg phosphorus/ha to the absence of infection significantly and the removal of the beneficial effect of the mycorrhizal infection.

The reason for the decrease in mycorrhizal infection as a result of the increase in phosphorous levels was shown by Cooper [4] that under conditions of phosphorus deficiency, the amount of phospholipids in the membranes of root cells decreases, leading to an increase in the permeability of these membranes, and this leads to an increase in the root secretion of reducing sugars. And amino acids lead to the formation of mycorrhizae, thus increasing the percentage of infected roots, but under conditions of availability of phosphorus, and the permeability of the membranes of the roots cells decreases due to the increase in phospholipids in them, and as a result, the secretions of the roots decrease from reducing sugars and amino acids, and this leads to a decrease in the percentage of infected roots. The decrease in the rate of infection may also be due to the increase in the concentration of phosphorus in the tissues of the plant, and the reason can be attributed to the fact that high levels of phosphorus may reduce the concentration of carbohydrates in the roots of plants, and as a result, the rate of infection is reduced. In general, high soil fertility leads to less mycorrhizal infection, so it is unlikely that we will find many mycorrhizae in densely cultivated soils. However, some crops are highly infested with fungi even in very fertile soils, as mycorrhizae are found in all poor and rich soils. Therefore, a low level of fertility is not always a condition for a significant development for mycorrhizal.

#### *2.4.2 Temperature*

Studies have shown that temperature has an effect on the formation of spores and colonies in greenhouse conditions, as the temperature usually affects the increase of colonies and thus increases the spores. The ideal temperature of mycelium on the surfaces of the roots will be 20–30°C. As for the formation of spores and the species that form the spore cyst, it will be at its strongest at 35°C. Studies have shown that the succession and decrease of temperatures increases the formation of colonies as well as the spores. Yoh-ichi Matsubara et al. [5] found that after 7 weeks of inoculation at a temperature of 20/25°C, the infection level of *Gigaspora margarita* in roots was 63.0 and 20% in *Glomus sp.* RIO, and the infected plants gave with fungi the highest values of plant height, dry weight of the vegetative part, and phosphorous concentration in the vegetative and root parts compared to unpollinated plants, as the effect was more pronounced in *Gigaspora margarita* than *Glomus sp.* RIO, but after 11 weeks from vaccination and when the temperature drops to 15°C, the infection level was recorded at 48.9% in *Gigaspora margarita* and 58.9% in *Glomus sp.* RIO. The plants infected with the fungus showed the highest values in all studied traits compared with the uninoculated ones. While after 11 weeks of insemination and at a temperature of 30°C, the infection level was 66.3% in *Gigaspora margarita* and 36.7% in *Glomus sp.* RIO.

#### *2.4.3 Light*

Light can indirectly affect soil microorganisms through its effects on plants, whose photosynthetic products are released from the roots [6]. The penetration of light through soil is important because of its effects on factors of ecological significance, such as spore germination, root growth, fungal growth, and formation of mycorrhizal and leguminous nodules. Light penetration can be affected by soil moisture content, soil type, cover material, and particle size. Phytochromes that are biliprotein photoreceptors enable some microorganisms to adapt to the light regime in the soil [7].

Fungi are unable to use light for photosynthesis; however, radiation plays a role in the biochemical and morphological responses of some fungi such as *Phycomyces blakeslleanus*, including their growth and differentiation. Physiologically and ecologically, a significant amount of light penetrates the soil approximately 4–5 mm from the surface, eliciting some phototrophic responses in plant roots. This information has led some VAM experts to hypothesize the function of LED on VAM formation. The induction of hyphal growth by light and chemicals, for example, the effect of blue light on hyphal branching, has been reported [8]. These authors demonstrated that blue light and some exudate components effectively stimulate hyphal branching, suggesting the involvement of a second messenger responsible for this synergism. The photo-induction caused by photo-mimetic compounds has been studied in many other fungi as well [9].

It is important to assess some environmental factors that stimulate hyphal growth and sporulation, such as root exudates, and LEDs applied individually and in combination. Lighting from red LED or red+blue LED could stimulate hyphal growth in *G. margarita* and *Glomus* spp. (R-10) *in vitro* [10]. Moreover, VAM colonization of corn roots was improved when the rhizosphere was exposed to light. The marginal VAM colonization of chalk false-brome [(*Brachypodium pinnatum* (L.) P.B.)] under shade conditions could show that when low light limits photosynthesis and thus growth of the plants, they dispense with the colonization of VAM in order to save the expenditure of organic carbon [11].

Previous studies have reported the effects of blue light on hyphae; however, its synergistic effect with root exudates on the production of new spores with minimum soil residues is still unclear. In this factor (light), two variables must be distinguished: (1) the period of illumination and (2) the intensity of illumination. The length of the illumination period is 32 hours, and the length of the illumination period is more important than its intensity in the formation of colonies. The growth of mycorrhizal onion plants was under light intensity of LUX 25,000 compared to LUX 13,000 and for 16 hours of light (23°C) with 8 hours of darkness (14°C) [12, 13].

#### *2.4.4 The pH*

Studies have shown that the reaction number pH has a significant effect on the mycorrhizal fungi, as well as the type of VAM plays a role in determining the appropriateness of the type of interaction, as it was found that *G. mosseae* excels in alkaline soils, most of the soils of Iraq work on this quality because it prevails in alkaline soils, and it can germinate its spores at a certain extent a broad range starts from 6 to 9, while we find that the species *Gigaspora coralloida*, which was isolated from acidic fluoride soils, its spores germinate at pH 6–4, and according to this we find that the *G.mosseae* is more suitable for alkaline media than the *Gigaspora coralloida*, and it was found that the type *G.epigaeum* has the ability to grow its spores in a wider range than the previous two species, which is from 6 to more than 8. On the other hand, it was found that both types of mushrooms *G. intaradices* and *G.mosseae* can grow in different types of soils, but they grow better in neutral and alkaline soils, while the fungus *Gigaspora margarita* prefers acidic soils. Therefore, it can be said that the pH affects the germination of VAM spores, and it is worth noting that there is a kind of fit between the pH appropriate for the growth of the plant host and the pH appropriate for the growth of the VAM.

To test the response of arbuscular mycorrhizal (AM) fungi to a difference in soil pH, the extraradical mycelium of *Scutellospora calospora* or *Glomus intraradices*, in association with *Plantago lanceolata*, was exposed to two different pH treatments, while the root substrate pH was left unchanged. Seedlings of *P. lanceolata*, colonized by one or other of the fungal symbionts, and nonmycorrhizal controls, were grown in mesh bags placed in pots containing pH-buffered sand (pH around 5 or 6). The systems were harvested at approximately 2-week intervals between 20 and 80 days. Both fungi formed more extra radical mycelium at the higher pH. *Glomus intraradices* formed almost no detectable extraradical mycelium at lower pH. The extraradical mycelium of *S. calospora* had higher acid phosphatase activity than that of *G. intraradices*. Total AM root colonization decreased for both fungi at the higher pH, and high pH also reduced arbuscule and vesicle formation in *G. intraradices*. In conclusion, soil pH influences AM root colonization as well as the growth and phosphatase activities of extraradical mycelium, although the two fungi responded differently [14].

#### *2.4.5 Salinity*

Several studies indicated that salinity has an important effect on the percentage of mycorrhizal infection and spore germination. These studies showed that there is a negative correlation between the incidence of infection, the number of spores, and the soil content of sodium when the Na concentration range is reached from 153 to 11,600 ppm, and it has been observed that 1 VAM fungi completely disappear when the concentration of Na increases to 3181 ppm. There are many studies that dealt with

#### *Factors Affecting Mycorrhizal Activity DOI: http://dx.doi.org/10.5772/intechopen.108099*

this subject, which showed that the salt concentrations are higher than 4 dSiemens. m2 in the root zone of the plant has caused a significant reduction in the infection rate for all mycorrhizal fungi, whether the addition of mycorrhizae with seeds or with seedlings, but the fungus *G. mosseae* recorded the highest rate of infection as an average at a higher salinity level than the rest of the species. The roots of tomato plants have caused a significant reduction in the incidence of infection with each type of mycorrhizal fungi and in the two ways of adding the inoculum (with seeds and with seedlings), area M. However, the fungus *G. mosseae* recorded the highest rate of infection as an average at each salinity level compared to the rest of the types and with both methods of additions to vaccines.

The process of spores of mycorrhizal fungi goes through four phases: the hydration phase, the activation phase, the emergence phase of the germination tube, and the hyphae growth phase. The failure of one or more of these phases due to high concentrations of dissolved salts in the soil solution may delay or stop the growth and development of the host plant. Three sources of salts (sodium chloride, sodium nitrate, and potassium chloride) with different concentrations were used to study their effect on spores' germination components of five types of endophytic mycorrhizae in three separate experiments. The fungus *G. mosseae* was significantly superior to the rest of the spores' germination components of other fungi, and the percentage of mycorrhizal spores germination decreased significantly when exceeding the critical concentrations of sodium and chlorine ions. Germination or inhibition of the germination process is by the toxic effect of sodium and chlorine ions. The toxic effect of sodium ion was more than the toxic effect of chlorine ion on the germination process, and in a study by Al-Khaliel [15], he used five levels of calcium carbonate (20, 30, 40, and 50%) and five levels of calcium sulfate (5, 15, 25, and 50%) to find out their effect on the components of spore germination of five types of mycorrhizal fungi. The results showed that the high levels of calcium carbonate (40 and 50%) and calcium sulfate (15, 25, and 50%) reduce the percentage of germination and other components of germination, but the effect differs according to the Mycorrhizae genus Glomus and Gigaspora, as well as between species within the genus Glomus, and the critical level of calcium carbonate is 20–30% and for calcium sulfate is 5–10% which after it is exceeded, the percentage of germination and other components of germination decrease, and they attributed the reason for the decrease in the percentage of germination to the lack of availability of nutritional needs of phosphorus and other elements due to the high percentage of calcium carbonate and sulfate, as well as due to the harmful effect of calcium and sulfate ions in the soil.

On the other hand, there are studies that showed that mycorrhizal fungi naturally appear in saline environments, despite the little affinity between mycorrhizae and halophytic plants such as hypophysis. The results of the research were that 21 of the 89 plants of the halophytic species were infected with VAM fungi, which indicates that the VAM works within saline concentrations, and 11 of the 89 plant species developed spores in the rhizosphere. This is sufficient evidence that different plants of 21% have an infection and 11% have an infection and spores. Al-Khaliel [15] found that the number of mycorrhizal spores did not decrease significantly with the increase of soil salinity, and the rate of spores was 100 per 100 g of dry soil, and that the majority of mycorrhizal species that were found in the soil of the plain whose salinity reaches 160 dSm are *G.etunicanum*, *G.versifform*, and *G.intraradices*, and this was attributed to stimulating the formation of spores under salt stress, meaning that the mycorrhizae is the reason for the production of spores at low levels of root infection under saline stress conditions, which inhibits the formation of mycorrhizae from spores and then the accumulation of spores in the soil.

#### *2.4.6 Second: Biological factors*

The biological interaction between mycorrhizal and other organisms took the space and thought of many researchers, and the matter of the fact is that the first to approach this topic and define the characteristics of the region in which this interference occurs is Hiltner [16] when he called the region surrounding the root hairs the rhizosphere region, which is the region affected by many factors, including the number of living organisms and growth and secretions of the roots, and he identified in an unequivocal way that the activity of organisms in this area is at its highest, and therefore it is not surprising that it is said that it is the key to microbiology to take its scope in maximizing plant production. And some are reduced, and some are free, and some are restricted. When there is an agreement between the plant and the living organism, the response is the greatest, and when there is no agreement between the plant and the living organism, the ability of the plant to grow and absorb is determined, and therefore the living organisms do not play the required role and mediate to facilitate the elements. In this area, there are mucilage, sloughed cells, and a wide quantitative production of enzymes, hormones, and growth regulators, in addition to antibiotics and multiple sugars, and all of these are diagnosed and studied, and thus the rhizosphere area has an applied importance from an agricultural point of view because it represents the true cradle of seeds and the roots in them and the increase in the activity of organisms in them. The interference between organisms, which is the effect of one organism on the activity, growth, and reproduction of another organism, and the interference is either:


The unsatisfactory interactions that are of different types, including:

	- a.Rhizobia and leguminous plants (symbiotic specialty).
	- b.Mycorrhizae and plants (nonspecialized).
	- c.Azotobacter or azospirilm and the plant (associative).

There are some organisms that are involved in the so-called Commelizan effect when two organisms are present with each other, so one of them stimulates the other. For example, the presence of mycorrhizae with Azotobacter increases the

#### *Factors Affecting Mycorrhizal Activity DOI: http://dx.doi.org/10.5772/intechopen.108099*

rate of cytoplasm release and thus enables plants to live in low levels of iron with no symptoms of deficiency. Many researches and studies indicated the effect of various microorganisms groups, especially bacteria, on the germination and growth of arboreal mycorrhizal fungi. Bacteria increase mycorrhizae by removing the inhibitor, such as self-inhibitors of the fungi spores or the production of chemicals that stimulate the growth of the spores, as well as an increase in plant secretions by increasing the permeability of the membranes and thus an increase in the growth of fungi and their ability to penetrate the host (we will address the relationships between mycorrhizae and other soil microbiota in other topics from this chapter). It was found that mung bean yellow mosaic virus reduced the rate of mycorrhizal infection and the production of spores by the fungi *Glomus constrictum*, *G. Fasciculatum*, and *Acaulospora morrowede*, but fungi *Gigaspora gilmorei* could not form any mycorrhizal roots in plants infected with the virus compared to healthy plants.

There have been many attempts for years that have been concerned with studying the state of competition between the mycorrhizae introduced into the growth medium (the rhizosphere) and the endemic mycorrhizae. Taking into account a number of variables, the most important of which is the rate of infection in the roots and then the calculation of the mycorrhizal roots, as well as knowledge of the formation of spores after adding VAM to the growth medium. Accordingly, the type of added vaccines will have two types of effects: either a positive effect or a negative effect (competition), the positive effect may increase the incidence of infection and spores and increase the production of spores due to the positive effect of one organism on another organism. Studies have shown that there is another type of competition that arises between the types of VAM introduced into the growth medium. And the technique that determines how this antagonism occurs between organisms is either the use of biochemistry and reliance on the metabolites secreted from living things and determining their structures, or the use of genetic engineering to determine this type of antagonism. Mycorrhizal fungi coexist with multiple plant families, and there are other families with a low tendency for this type of symbiosis, and most families have a high susceptibility to mycorrhizal infection, but some species such as cruciferous and ramiform do not infect mycorrhizal. Studies have shown that the history of vegetation cover in a region may participate in determining the density of mycorrhizal presence and in many times the supremacy of one sex over another.
