Modulation of Plant Micronutrient Uptake by Arbuscular Mycorrhizal Fungi

Abstract

Plants require light, water, and nutrients for better growth and reproduction. Arbuscular mycorrhizal (AM) fungi associate with root systems of most land plants and improve plant growth by enhancing the uptake of soil nutrients, including micronutrients. Contradictory influence of mycorrhizal plants in micronutrient uptake may be due to different edaphic conditions, which affect AM fungal root colonization and extraradical hyphal development. The micronutrient uptake of plants is influenced by different factors like availability of macronutrient like phosphorus (P) and micronutrients themselves in soil. AM fungal hyphal growth and root colonization are suppressed by high levels of micronutrients in soil. In soils the mobility of Cu, Zn, Mn, and Fe is low, and uptake by roots is restricted by low diffusion rates and root depletion zones created by plant roots. AM plants overcome this by exploring large volume of soil compared to roots and minimize the diffusion distance to enhance the availability of these immobile nutrients. Uptake of Cu and Zn or Mn and Fe is quite different. The uptake of Cu and Zn is affected by amount of plant and soil P levels, whereas the uptake of Mn and Fe is affected by indirect reduction of oxidation-reduction potential and availability of Mn and Fe in mycorrhizosphere. Under stress conditions, AM fungi help plants to increase their nutrient uptake, thereby imparting tolerance to prevailing stress. This is seen especially under saline conditions where AM fungal application limits the Na+ and Ca2+ ion concentration in plants by enhancing Mg2+ uptake, thereby increasing chlorophyll concentration, photosynthetic efficiency, and plant growth. AM fungi are potential tool for improving plant health and rhizosphere for better uptake of micronutrients under various edaphic conditions.