Root Exudates and Their Importance in Arbuscular Mycorrhizal Symbiosis and Nutrients Navigation from Inaccessible Soil: An Efficient Mediator of Mineral Acquisition in Nutrient Deprived Soil

The growth and development of plants happen through internal molecular communications that rely on adequate nutrient supplements to roots from the soil. Plants take mineral nutrients from the rhizosphere, where the microbes interact with plant root exudates. The root exudates secreted by the plants into the rhizosphere have a pivotal function in mediating the relationship between plants and soil microbes. These metabolites from plant roots have different responses toward soil organisms and modify their composition and activity. Plants utilize root exudates to balance the role of mineral nutrient transporters in recognizing the availability of nutrients and further the direct supply of nutrients depending on the demand. The root exudates are affected by fungal communities associated with the roots depending upon their abundance and composition. Root exudation commences and regulates the communications channel between plant roots and the associated soil microbes like arbuscular mycorrhizal (AM) fungi. In addition, the root exudates act as signals that instigate the establishment of AM symbiosis. During the pre-symbiotic phase, some metabolites secreted by roots are necessary for AM fungal spore germination, hyphal growth, and root colonization. The metabolites in the root exudates are sensed by AM fungi, and these metabolites may be stimulatory or inhibitory to the symbiotic establishment. In this chapter, we highlight the role of root exudates in plant nutrient availability, the establishment of AM symbiosis, and also the influence of AM fungi on plant root exudates.