Microbes-Mediated Facilitation of Micronutrients Uptake by Plants from Soil Especially Zinc

Abstract

Micronutrients are essential minerals required for the development of plants and humans, but they are often lacking in soils and food crops. Despite the fact that soils might contain substantial amount of micronutrients, their bioavailability in rhizosphere could be controlled by the combined effects of several edaphic factors, such as competing cations, anions, organic matter, pH, soil morphology, soil parent materials and biological factors, including plant characteristics as well as interaction of plant roots with microorganisms. Plant growth-promoting microbes belonging to cyanobacteria, bacteria, fungi and mycorrhizae can influence micronutrients availability by the process of solubilization, chelation and oxidation-reduction reactions in soil. Some microorganisms activate the release of root exudates by interacting with the plant roots. Moreover, their amount as well as composition affects the microbial diversity and activity of plant-associated beneficial microorganisms which ultimately affect the nutrient availability. Exuded carboxylates, that is, organic acids, may have role in solubilization of mineral nutrients as well as growth substrates for microbes. Some typical organic acids (such as lactate, citrate, acetate and oxalate) are found in the root exudate, which can convert the micronutrients in the plant-available forms to be transported across the plasma membrane of the root cells. Since soil microbial flora are not nutrient deficient in low-nutrient soil, they may be helpful towards increasing the soil micronutrient availability, plant uptake and also its accumulation in grains, that is, biofortification in a range of crops. This chapter describes the physiological importance of micronutrients in plants as well as improvements of nutrient uptake and utilization by plant systems.