**6. Final considerations**

**3.5. Phosphate solubilizing bacteria**

20 Grasses - Benefits, Diversities and Functional Roles

very low solubility compounds in the soil [63].

*Bacillus*, and *Penicillium* strains [66] have been reported.

**4. Mycorrhizae**

Together with N and K, P is one of the required macronutrients for the cultivation of grasses, whose content concentration is always lower than N and K. However, it is commonly neces‐ sary to use a great amount of phosphate fertilizers in agricultural crops, because in spite of the soils contain a large amount of P their availability to the plants is very little as P tends to form

Phosphorus is an essential element to grasses, since it is necessary and irreplaceable for the com‐ position of ribonucleic acids (RNA) and deoxyribonucleic acids (DNA), responsible for the trans‐ mission of the genetic code to the plants, protein production, and other essential compounds for

this nutrient unavailable to the plant. Some of the soil bacteria are important in the process of

Inorganic phosphate‐solubilizing microorganisms excrete inorganic acids and protons asso‐ ciated to these acids, which directly dissolve the insoluble phosphate, or chelate the cations with the phosphate anion [64]. Among phosphate‐solubilizing bacteria, *Burkholderia* [65],

Mycorrhizal fungi are associated with roots of plants and play an important role in the soil phosphorus cycling as extensions of the root system, increasing the absorbing area of the root and the absorption rate of phosphorus. The mycorrhizal association does not substitute phos‐ phate fertilization, but efficiently increases the use of phosphorus or an added compound through fertilization [67]. Grasses such as maize, sorghum, wheat, rice, and cultivated forage

**5. Fungi of the genus** *Trichoderma* **and the biological control of diseases**

Fungi of the genus *Trichoderma* are biological control agents that act against phytopathogenic edaphic fungi, however, colonizing plant roots to stimulate plant growth and protect them against infections. Root colonization often increases root development, crop productivity,

Fungi present different mechanisms to controlling and suppressing the soil's phytopatho‐ gens, such as mycoparasitism, antibiosis and antagonism [70]. In addition, *Trichoderma* strains are active in the production of fungal cell walls, enzymatic degradation, including pectinases,

Compared to the chemical control, the use of biological substances to control soil diseases is beneficial, since it does not induce resistance from the target organism, effectively controlling

PO<sup>4</sup> −

and HPO<sup>4</sup>

(PO<sup>4</sup> ) 2 ) make

2−, just

the plant structure and seedling production. Grasses absorb soil P as H<sup>2</sup>

like other plant species; thus, insoluble phosphates like tricalcium phosphate (Ca<sup>3</sup>

dissolving these insoluble solutions, facilitating the access to this essential nutrient.

grasses may have their roots naturally colonized by mycorrhizal fungi [68].

resistance to abiotic stresses, and improved nutrient use [69].

cellulases, and chitinases, involved in the biological control [71].

Soil microorganisms are able to influence the establishment and yield of grasses by means of sev‐ eral mechanisms. The nutrients cycling by soil microorganisms, the biological nitrogen fixation by associative bacteria, phytohormones production by soil bacteria, and the acquisition of phosphorus by mycorrhizal fungal hyphae networks are just some examples of direct mechanisms of beneficial interaction between soil microorganisms and cultivated grasses. As examples of indirect mecha‐ nisms, we can mention the suppression of pathogens by mechanisms of predation or competition, as we also discussed. Given this wide range of mechanisms presented by microorganisms for the benefit of cultivated grasses and consequently of the human benefit, it is imperative that these mechanisms are well studied to be inserted in systems of conservationist agriculture, which must obtain the maximum agronomic yield of the crops, allied to the rational use of natural resources.
