# Fungi of the _Trichoderma_ Genus: Future Perspectives of Benefits in Sustainable Agriculture
## 5 Application of _Trichoderma_ Fungi in Promoting Plant Growth
### Increasing the Availability of Nutrients  
The ability of _Trichoderma_ to produce siderophores under conditions of poor iron availability is not only a mechanism of competition for nutrients with other microorganisms but is also responsible for stimulating plant growth [21; 62]. The formation of soluble forms of iron enables plants to absorb Fe\({}^{2+}\) ions through the root system and then use them for proper growth and development [32; 34]. This element also acts as a cofactor necessary for the activity of enzymes such as cytochrome P450, catalases, and peroxididases which protect the plant from the toxic effects of hydrogen peroxide [139]. [PERSON] and [PERSON] [136] documented that species _T. asperellum_, _T. atroviride_, _T. harzianum_, _T. konnigii_, _T. longibrachiatum_, _T. reesei_, and _T. virens_ produced siderophores in the range of 20.69-91.68%. An example of a compound that, by chelating iron ions, exhibits the ability to promote plant growth is harzianic acid (HA). [PERSON] et al. [140] analyzed the effect of HA produced by _T. harzianum_ on tomato growth. The results showed that treatment of plants with harzianic acid induced seed germination, shoot, and root length by 76% and 66%, respectively, compared to the control. In addition, it was found that despite the low concentration of iron in the environment, the use of siderophores increased the concentration of this element in tomatoes. [PERSON] et al. [121] proved that a purified siderophore eluent produced by _T. asperellum_ affected the growth of cucumber seedlings. The treatment of plants with the mixture induced increases in root and leaf length and fresh weight by 57.4%, 23.3%, and 33.7%, respectively. It was also found that inoculation cucumber plants with the tested strain enhanced the Fe\({}^{2+}\) ion concentration in leaves by 19.5% compared to the control. The basic nutrient necessary for the proper functioning of plants is nitrogen. This element is a structural element of amino acids, proteins, and nucleic acids, as well as enzymes and chlorophyll, which are necessary for photosynthesis [141]. According to [PERSON] [142], properly conducted photosynthesis leads to an increase in the yield and dry weight of cultivated plants. In addition, an appropriate level of nitrogen reduces the aging process and chlorosis of the leaves, which has a positive effect on the morphological characteristics of the plants [141]. [PERSON] et al. [143] showed that _T. virens_ enhanced nitrogen uptake for both lettuce and rocket by 51% and 59%, respectively. [PERSON] et al. [144] reported that compared to the control, soil treatment with _T. viride_ resulted in an increase in nitrogen content of 1.8% in shoots and 1.28% in broccoli roots. Similarly, [PERSON] et al. [145] demonstrated that inoculation of tomato seeds with two strains of _T. harzianum_ enhanced the ability of the plants to extract nitrogen ions from the soil. In the control sample, the uptake was 1.31%, while the use of _Trichoderma_ isolates increased nitrogen uptake to 2.27%. The main macroelement necessary for proper plant development is phosphorus, which is a component of enzymes, cofactors, and biomolecules [58; 34]. In addition, this element participates in the process of photosynthesis, fruit ripening, and nitrogen binding. Plants are only capable of absorbing phosphorus in the form of soluble anions H\({}_{2}\)PO\({}_{4}\)\({}^{-}\) and HPO\({}_{4}\)\({}^{2-}\), which have an average soil content of only 0.1%. The remainder of P is in the form of insoluble salts of iron, aluminum, and calcium or specifically adsorbed on clay colloids. _Trichoderma_ sp. has developed mechanisms of phosphate solubilization and mineralization, responsible for converting unavailable forms into orthophosphate ions, which can then be absorbed by plants [146; 147; 148]. [PERSON] and [PERSON] [136] found that species _T. asperellum_, _T. atroviride_, _T. harzianum_, _T. konnigii_, _T. longibrachiatum_, _T. reesei_, and _T.