Rhizospheric Plant-Microbe Interactions: Key Factors to Soil Fertility and Plant Nutrition

Abstract

Plant roots radiate a wide range of potentially valuable small molecular weight compounds into the rhizosphere which play a key role in the chemical, physical, and biological interaction between roots of the plants and the rhizosphere. The microorganisms present in the rhizosphere react with the numerous metabolites released by plant roots by positive, negative, and neutral ways, and these interactions may influence the plant growth and development, change nutrient dynamics, and also alter the plants susceptibility towards diseases and abiotic stresses. The root produces chemical signals that attract the bacteria and other microbes towards it. Beside this, positive interactions also include growth regulator mimics that support the plant growth and the cross-species signaling with other rhizospheric microorganisms. Plant-microbe interactions can influence the plant growth by providing nutrients and increased biotic and abiotic stress tolerance. Most of the agricultural soils have large amounts of inorganic and organic phosphorus (P), but it is present in immobilized form so is usually unavailable to plants. One of the major reasons why P is not readily available to plants is because of the high reactivity of P with some metal complexes. In this regard, the soil inoculants such as fungi, plant growth-promoting rhizobacteria (PGPR), and mycorrhizal fungi play a significant role in the solubilization of inorganic phosphate and mineralization of organic phosphates into easily available form to plants. Similarly, nitrogen (N) fixers provide available N to the plants. N is a key limiting factor in any ecosystem. For treating heavy metal-contaminated tailings and soils, bioremediation is one of the cost-effective methods and is emerging as the potential tool for removal of these contaminants from the soil or water. Bioremediation is a versatile process that could be applied in situ or ex situ manner. A wide variety of microorganisms such as bacteria, fungi, yeasts, and algae are being used in bioremediation processes, and some of these have already been employed as biosorbents of heavy metals. Various technologies such as phytoremediation, bioventing, bioleaching, land farming, bioreactor, composting, bioaugmentation, rhizofiltration, and biostimulation are nowadays used for the bioremediation of contaminants from the soil. The aim of this chapter is to focus on the plant-microbe interactions responsible for the maintenance of soil fertility, plant nutrition, and also the remediation of contaminated soil for sustainable agricultural