Adsorption of humic substances on ferrihydrite affects its use as iron source by plants

Authors

• Ana de Santiago Agrarian Research Institute Finca La Orden-Valdesequera
• Ana Maria Garcia-Lopez Agroforestry Science Department, University of Seville
• Ramiro Recena Agroforestry Science Department, University of Seville
• Maria Teresa Moreno Agroforestry Science Department, University of Seville
• Eusebio Carmona Agroforestry Science Department, University of Seville
• Antonio Delgado Agroforestry Science Department, University of Seville

DOI: https://doi.org/10.23986/afsci.95408

Abstract

Poorly crystalline Fe oxides are sources of Fe to plants. The adsorption of humic substances (HS) on these oxides alters its reactivity and stability in soils, and thus may affect Fe mobilization and uptake by plants from these compounds. This work aimed at studying how the adsorption of HS on Fe oxides affects its use as Fe source by two plant species with different Fe acquisition strategies, white lupin (Strategy I) and wheat (Strategy II). To this end, two completely randomized experiments, one with each plant, were carried out using a calcareous growing media and involving increasing amounts of HS adsorbed on ferrihydrite (0, 16, 60, and 97 mg C g^–1) which was used as Fe source. The highest HS rate was the only treatment that significantly increased Fe uptake in wheat relative to control without HS. This was related to a decreased concentration of Fe in poorly crystalline oxides in the growing media. On the contrary, HS did not affect significantly Fe uptake by lupin. However, in this crop, the highest HS rate decreased the concentration of Fe in oxides relative to the lowest HS rate, without significant differences with other treatments. Thus, the effect of adsorbed HS on Fe uptake differed in two plants with different Fe acquisition strategies. The increased Fe uptake in wheat at the highest HS rate can be explained at least in part by an increased Fe mobilization from oxides by plant roots. These findings provide new insights on the role of soil organic matter on plant Fe nutrition.