The Role of Low Molecular Weight Organic Acids in Micronutrient Bioavailability in Soil

Bioavailability of micronutrients in soils and their uptake by plants depend on soil properties (e.g., pH and carbonate content) and the interactions between plant roots and soil microorganisms. The low bioavailability of iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn), as a major factor limiting plant nutrition, in calcareous soils is due to the low organic content, high pH levels, and precipitation by carbonates in such soils. Study has shown that, under nutrient deficiency conditions, plant roots release low-molecular-weight organic acids (LMWOA) such as citric, oxalic, and malic acids to increase the solubility of micronutrients like Fe, Mn, Cu, and Zn in the rhizosphere. The LMWOAs exuded into the rhizosphere are known to enhance the mobility and bioavailability of such micronutrients and their uptake by plants. In addition, LMWOAs are involved in metal detoxification and improvement of microbial activity in soils. The present study investigates the role LMWOAs play in the bioavailability of such micronutrients as Fe, Mn, Cu, and Zn.