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.
Highlights
Iron (Fe) is an essential micronutrient for humans and plants
The increased Fe uptake in wheat at the highest humic substances (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
The objective of this work was to study how the adsorption of humic substances on ferrihydrite affects its use as Fe source by two species with different Fe acquisition strategy, white lupin (Strategy I) and wheat (Strategy II), grown in a calcareous growing media where Fe availability is supposed to be restricted by the basic pH
Summary
Iron (Fe) is an essential micronutrient for humans and plants. Despite being an abundant element in soil, its availability to plants is usually low due to the low solubility and slow dissolution of Fe compounds (Lucena 2003, Kraemer et al 2006, Lemanceau et al 2009). Humic sustances (HS) enhance Fe availability to plants by preventing its precipitation as Fe oxides (Schwertmann 1966, Olaetxea et al 2018), by formation of soluble complexes (Gerke 1993, Mackowiak et al 2001, Bocanegra et al 2006) which can move in the soil and reach the roots increasing Fe transport (Pandeya et al 1998, Cesco et al 2000, Garcia-Mina et al 2004, Chen et al 2004, Zanin et al 2019) and by its redox-reactive properties (Kögel-Knabner et al 2008). Iron complexed to soluble humic substances has proven to be an efficient Fe source for plants grown in nutrient solution (Pinton et al 1999, Cesco et al 2002, Bocanegra et al 2006)
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