**5.1 Fungi in plant nutrition**

The saprotrophic and AM fungi provide nutrition to the plants.AM fungi increase the growth and productivity of the plant by increasing nutrient uptake, mycorrhizae form mutualistic symbiotic relationships with plant roots of more than 80% of land plants including many important crops and forest tree species [52–54]. The two dominant types of mycorrhizae are ectomycorrhizae (ECM) and arbuscular mycorrhizae (AM) which can improve water and nutrient uptake and provide protection from pathogens but only a few families of plants can form functional associations with both AM and ECM fungi. However, AM fungi are most commonly found in the rhizosphere roots of a wide range of herbaceous and woody plants [49, 55]. ECM fungi help the growth and development of trees because the roots colonized with ectomycorrhiza can absorb and accumulate nitrogen, phosphorus, potassium, and calcium more rapidly and over a longer period than nonmycorrhizal roots [56]. ECM fungi help to break down the complex minerals and organic substances in the soil and transfer nutrients to the tree [54, 57]. AM fungi are a widespread group and are found from the arctic to the tropics and are present in most agricultural and natural ecosystems with different forms and structures see **Figure 5**.

#### **Figure 5.**

*Endomycorrhizae characterized by structures formed in the root cortex region (a) hyphae, vesicles, and spores in soybean roots (b) external spores (c) cluster of auxiliary cells outside the root.*


#### **Table 3.**

*Showing application of SMS and SMC in the different horticultural cultivars (source Singh et al. [41]); the positive indicates 'use' and a negative sign indicates 'not known'.*

Apart from the fungal biofertilizer and AM fungi, the spent left out after mushroom harvest are a good source of plant nutrition, the spent are commonly known as the Spent mushroom compost (SMC) or spent mushroom substrates (SMS) depending upon process and mushroom species of cultivation, mushroom compost has a major role in the integrated farm system [41, 58, 59]. The application of SMC and SMS have been evaluated on different cultivars which impart significant result in production and yield (**Table 3**).

SMC has organic matters that make them to be used in a large variety of crops including legumes crops such as *Vigna unguiculata* [66]*,* chickpea, pea, soyabeans [63].

#### **5.2 Wood wide web**

The evolution of the plant from the water to land some 500 million years ago could not have possible without striking up a relationship with fungi, today almost all plants depend on symbiotic mycorrhizal fungi and some completely depend on the fungal partners and lost the ability of photosynthesis (eg- *Voyria tenella*) and therefore these type of plant obtain their food from neighboring photosynthetic plant through the shared fungal network, shared network of mycorrhizal develops due to the ability of both plant and mycorrhizal fungi to form a relationship with multiple partners [67]. The plants which depend on fungi for its whole life are called as mycoheterotrophs, most of the *orchid* lives as mycoheterotrophs when they are young and later starts photosynthesis as grew older which is known as 'take now, *Biodegradation by Fungi for Humans and Plants Nutrition DOI: http://dx.doi.org/10.5772/intechopen.99002*

pay later'. A wide range of minerals is transported between plants through a shared network of mycorrhizal fungi. The notion that plants can 'talk' to one another is recently accepted in the mainstream of science, though the plant can not move but they pass their massages through chemical signal(volatile organic compounds) to another plant via a network of connection which is termed as the common mycorrhizal networks (CMN) formed by mycorrhizal fungi and different plants, and this is described as the below-ground internet network which is colloquially called as The Wood Wide Web [68]. The CMN integrate multiple plants and fungal species, that interact, provides feedbacks and adapt, and form complex adaptive social networks, the formation of these networks influenced by various factors, however, CMN provides communication facilities between plants principally by two forms of CMN- arbuscular and ectomycorrhizal, not only CMN provides connectivity among the plants but also provides facilities for the uptake of nutrition and distribution of minerals among the plants. CMN plays a crucial role in soil ecosystem management. It has been established that if a plant is attacked by the plant pathogens it sends the signal to the neighbor plants so that they can prepare themselves to fight against the pathogen by activating various defense mechanisms [68, 69]. Fungal hyphae as a network cable have far-reaching potential in the betterment of plant health systems, but not everything that is transmitted between plants is beneficial to individual plants because toxin (allelopathic chemical) may also be transported via a mycelial network. The whole system is very complex and holistic and research has emerged to understand this at the molecular level.
