Abstract
Many studies have shown the close relationship between the beneficial action of soil and sedimentary humic acids on the growth of plants cultivated in calcareous soils and their ability to improve Fe plant nutrition. These results have been ascribed to the humic acid (HA) capability to improve Fe solubility and bioavailability. However, other effects more related to a humic acid action on the specific mechanisms activated in roots of plants under Fe deficiency cannot be ruled out. Although this question has been studied in dicotyledonous plants, in graminaceous plants there are no specific studies. Here we investigate the ability of a humic acid extracted from peat (HA) to improve Fe nutrition in wheat plants cultivated under Fe deficient and sufficient conditions. The results show that HA can improve the physiological status of Fe deficient wheat plants by alleviating some of the deleterious consequences of Fe deficiency on plant development and increasing the plant ability to secrete phytosiderophores to the nutrient solution. This action of HA is associated with increases in the Fe-active pool in leaves that might be related to the mobilization of the Fe complexed by HA resulting from the interaction of HA with the phytosiderophores in the nutrient solution. The Fe translocation from the root to the shoot may be favored by the action of trans-Zeatin Riboside (tZR) since the leaf concentration of this phytohormone was enhanced by HA in Fe deficient plants.
Highlights
Iron (Fe) is a key element for energetic processes in plants, such as photosynthesis, respiration, nitrogen assimilation, and synthesis of plant enzymes (Barton and Abadia, 2006; Abadía et al, 2011)
The plant physiological status of Fe deficient plants treated with humic acid (HA) clearly improved as it was reflected in significant increases in chlorophyll content and net photosynthetic rates (Figures 2A, 3A)
Control Fe deficient plants supplied with the concentration of Fe contained in HA composition (12.5 μM Fe) did not experience these effects at the same level as that of Fe deficient plants treated with HA (Figures 2B, 3B)
Summary
Iron (Fe) is a key element for energetic processes in plants, such as photosynthesis, respiration, nitrogen assimilation, and synthesis of plant enzymes (Barton and Abadia, 2006; Abadía et al, 2011). The content of Fe is higher than that of any other microelement; its bioavailability is highly dependent on changes in the acidity and redox potential of the environment (Lucena, 2003). This fact favors its solubility in acidic soils. Fe deficiency is one of the major nutritional concerns lowering crop yield and nutritional quality, mainly in alkaline-calcareous soils, making up 30% of the world’s agricultural soils (Barton and Abadia, 2006; Abadía et al, 2011). The levels of Fe in soil solution can increase due to complexation of the micronutrient with soluble organic ligands like organic acids, phenols, phytosiderophores released by roots of graminaceous plants, microbial siderophores, and humified organic matter (Garcia-Mina, 2006; Zanin et al, 2019; Gerke, 2021)
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