Evaluation of palygorskite and sepiolite abilities to supply Mg for sorghum plants in presence/absence of Glomus mosae mycorhizae

Introduction Clay minerals are considered as the main source of ion exchange and storage of nutrients in the soil. Knowledge of change and transformation of minerals, in relation to plant nutrition, fixation and release of elements is important. Sepiolite and palygorskite are fibrous clay minerals widely distributed in arid and semi-arid soils. Both minerals are rich in Mg and therefore, their weathering can significantly affect the chemistry of Mg in soil. Biological weathering which is carried out by living organisms (i.e. plant roots, soil fungi and bacteria) plays an important role in providing nutrients to plants. Hence, the use of microorganisms such as mycorrhizal fungi in the rhizosphere of agricultural crops has become more widespread. In recent years several studies have been conducted in relation to the weathering of minerals in the rhizosphere soil. However, few studies in terms of mycorhizal symbiosis with plant roots were carried out on release of Mg from sepiolite and palygorskite. Therefore, a pot experiment with a factorial arrangement through a completely randomized design was conducted to identify how symbiosis of sorghum roots with Glomus mosae mycorhizae affects release of Mg from sepiolite and palygorskite.
Materials and Methods Pots containing sterile quartz sand and sepiolite or palygorskite (25-53 µm) were prepared and fungal treatments including presence or absence of fungus Glomus mosae were applied to the pots and then sorghum seeds were sown. Johnson nutrient solutions containing magnesium and without magnesium were used to feed plants during 70 days of experiment. After harvesting, the chlorophyll content, plants height and stem diameter were measured by SPAD, tape measure and caliper, respectively. Afterwards, the roots and shoots were separated and plants biomass and the percentage of roots colonization determined. Then, plants were oven-dried, ground, and the magnesium contents of them after extraction with 1M hydrochloric acid were determined using Agilent 7000 ICP analyzer. The chemical composition of palygorskite, sepiolite, and quartz sand was determined using X-ray fluorescence (XRF) and their mineralogical composition was determined using X-ray diffraction (XRD) approach.
Results and Discussion Analysis of variance for the main effect of treatments on plant height, stem diameter, shoot dry weight and root dry weight showed that the effect of different sources of magnesium on plant height, stem diameter and shoot dry weight was significant (P Conclusion In both sepiolite and palygorskite treatments, magnesium and chlorophyll content increased in symbiosis with fungi. This shows the positive effect of Glomus mosae fungus on release of Mg from these two minerals, especially sepiolite. Although, both sepiolite and palygorskite were able to provide enough amounts of Mg for sorghum plants, however, it seems that in long-term Mg released from sepiolite can more easily meet the need of plants when compared with palygorskite.