Availability of Mn, Zn and Fe in the rhizosphere

Abstract

This review paper critically assesses the literature on soil-microbe-plant interactions influencing availability of micronutrients in the rhizosphere. The emphasis is placed on Zn and Mn, but Fe is also covered to some extent.Micronutrient availability in the rhizosphere is controlled by soil and plant properties, and interactions of roots with microorganisms and the surrounding soil. Plants exude a variety of organic compounds (carboxylate anions, phenolics, carbohydrates, amino acids, enzymes, etc.) and inorganic ions (protons, phosphate, etc.) to change chemistry and biology of the rhizosphere and increase micronutrient availability. Increased availability may result from solubilization and mobilization by short-chain organic acid anions, amino acids and other low-molecular-weight organic compounds. Acidification of the rhizosphere soil increases mobilization of micronutrients (eg. for Zn, 100-fold increase in solubility for each unit of pH decrease).For diffusion-supplied micronutrients, the uptake rate is governed by the soil nutrient supply. Fertilisation with micronutrients (more so in case of Zn than Fe) can be effective in increasing the concentration of micronutrients at the soil-root interface. In addition, micronutrient-efficient crops and genotypes can increase an available nutrient fraction and hence increase micronutrient uptake.Our understanding of the physiological processes governing exudation and the soil-plant-microbe interactions in the rhizosphere is currently inadequate, especially in terms of spatial and temporal variability in root exudation as well as the fate and effectiveness of organic and inorganic compounds in increasing availability of soil micronutrients and undesirable trace elements. The interactions between microorganisms and plants at the soilroot interface are particularly important as well obscure.

Iron and zinc levels in Vigna unguiculata (L.) Walp under varying phosphorus and fixed nitrogen treatment conditions

“…However, micronutrient-deficient soils are widespread; many millions of hectares of arable land worldwide are deficient in one or more micronutrient elements (Rengel, 2015). Further compounding this is the low phosphorus (P) utilization efficiency of the cowpea (Emechebe, Singh, Leleji, Atokple, & Adu, 1991).…”

“…In addition, legumes store P as phytate (PA) which, together with inositol penta phosphate, is one of the main inhibitors of Zn absorption (Kaya, Küçükyumuk, & Erdal, 2009). For diffusion-supplied micronutrients, the uptake rate is governed by the soil nutrient supply, and fertilization with micronutrients (more so in case of Zn than Fe) can be effective in increasing the concentration of micronutrients at the soil-root interface (Rengel, 2015). There are growing concerns, however, that the emphasis on increasing cereal yields by the application of macronutrients alone may lead to deficiencies of micronutrients, mainly Fe and Zn, and also vitamins, in diets of the poor who rely on a cereal-based food supply (Graham & Welch, 1996).…”

“…This study and cowpea is also at the heart of the fight against micronutrient deficiency due to its ability to accumulate Fe and Zn in both grains and leaves (Mamiro, Mbwaga, Mamiro, Mwanri, & Kinabo, 2011).However, micronutrient-deficient soils are widespread; many millions of hectares of arable land worldwide are deficient in one or more micronutrient elements (Rengel, 2015). Further compounding this is the low phosphorus (P) utilization efficiency of the cowpea (Emechebe, Singh, Leleji, Atokple, & Adu, 1991).…”

Effects of zinc fertilizer rate and application method on photosynthetic characteristics and grain yield of summer maize

“…It has been reported that basal Zn fertilizer may have a strong residual effect (Liu et al, 2004), but in some soils, Zn can be fixed and is therefore not utilized by the crop (Rengel, 2015).…”

Xylem sap mineral analyses as a rapid method for estimation plant-availability of Fe, Zn and Mn in carbonate soils: a case study in cucumber

“…In such soils, CaCO 3 is a major component which buffers soil solution pH at 7.5−8.5, due to a high bicarbonate concentration (HCO 3 -) (Lindsay, 1995). It is generally thought that soil pH governs plant-availability of many soil microelements, including Fe, Zn and Mn, and distinct effects of the prevailing rhizosphere pH on the availability of these three micronutrients were found (Sarkar and Wyn Jones, 1982;Rengel, 2015). Ferric (Fe 3+ ) and ferrous (Fe 2+ ) activity in the soil solution decrease 1,000-fold and 100-fold, respectively, for each unit increase in soil pH (Lindsay, 1995).…”