The Ability of two Plant Species to Uptake of Iron from Substrates Containing Muscovite and Phlogopite

Iron is one of the essential micronutrients for plant growth. The total amount of iron in soil is often more than plant iron requirement, but the low solubility of iron compounds in many of soils leads to low uptake of this element by plant and eventually, results in iron deficiency symptoms in plant. Iron is the structural component of cytochromes, leghemoglobines and ferredoxins. This element participates in many vital activities of plants, such as photosynthesis, respiration and fixation of molecular nitrogen. Some of micaceous minerals including muscovite and phlogopite which contain significant amounts of iron are plentiful in soils of arid and semiarid regions of Iran. The purpose of this study was to evaluate the ability of two plant species (alfalfa and barley) to uptake structural iron from muscovite and phlogopite.
The greenhouse experiment was conducted as factorial arrangement based on completely randomized design with three replicates. Treatments consisted of two plant species (alfalfa and barley), two types of micaceous minerals (phlogopite and muscovite) and two nutrient solutions (complete and iron-free).The experiment was done in 700 g pots containing a mixture of quartz sand (as the filling material), cocopeat and micaceous minerals (phlogopite and muscovite). Quartz sand and micaceous mineral were obtained from a mine near Hamadan City in Iran. For this purpose, X-ray elemental analysis fluorescence (XRF) was used to investigate the possibility of using quartz sand and micaceous mineral. Micaceous minerals were passed through a 140 mesh sieve and then, samples were saturated with Ca using a 0.5 M CaCl2 solution. To remove the excess Cl, saturated minerals were washed with distilled water several times and then samples were oven dried at 105 °C. Pots were filled with a mixture of 600 g quartz sand, micaceous mineral and cocopeat. The amount of mineral was added until there was 0.35% K2O in all pots. Two barley and alfalfa seeds were planted in each pot. During the growth period (150days), plants were irrigated and fed with distilled water and nutrient solutions, respectively. At the end of the growth period, shoots and roots of plants were harvested andiron contents of plants extracts were measured by atomic absorption.
For two plant species, the results showed that iron concentration in the pots containing phlogopite and fed with iron-free nutrient solution was in a sufficient range for both barley and alfalfa. The amount of iron uptake by alfalfa in both substrates and nutrition solutions was more than barely. It seems that alfalfa is able to uptake more amount of iron due to the abundant root exudates. The highest amount of iron uptake by root is related to alfalfa cultivated in substrates containing phlogopite and fed with iron-free nutrient solution. The highest barley shoots weight is related to substrates containing phlogopite and muscovite fed with complete (with iron) nutrient solution, whereas in alfalfa, the highest shoot weight is related to phlogopite-containing substrates fed with iron-free nutrient solution. Plants cultivated in two substrates containing phlogopite and muscovite did not show deficiency symptoms until late growth period and appearance of plants fed with iron-free nutrient solution was completely similar to those fed with complete nutrient solution. The amount of iron uptake by roots is several times higher than that of shoots. High uptake of iron by plant roots are affected by phytosiderophores produced by plant roots. Phytosiderophores produce chelate Fe (III) in the rhizosphere. These chelates are absorbed into the apoplast of roots and Fe (III) is separated from them as a result of certain reactions, and takes the path to xylem.
The results of this study indicate that iron structural phlogopite and muscovite minerals can provide iron requirement for plant during the growth season. Since phlogopiteis a tri-octahedral mineral, it has more Fe (II) and its structure is weaker than muscovite, and hence, is able to provide more iron for the plant during growth season. But muscovite is di-octahedral and its structure contains Al, so octahedral may not easily release its elements into the rhizosphere for the plants utilization. The factors influence the release of elements from micaceous minerals are structure and type of mineral. Alfalfa is able to release more iron from micaceous minerals thanks to its root systems and ability to produce more shoot. Since micaceous minerals have considerable amount of iron and are able to provide iron requirement for plant during growth season, it is recommended to investigate whether micaceous minerals are able to supply this element for longer growth periods.