Determination of Aluminum and Nutrient Levels in Plants

Aliquots of the supernatants were taken for the determination of the Al concentration in nutrient solutions. The roots and shoots were dried at 50 °C, combined into one sample for each pot, and ground to a powder. All samples were digested in a mixture of concentrated HNO₃ and 38% H₂O₂ at 70 °C using the digestion system DigiBlock (LabTech, Sorisole, Italy). The content of Al and the nutrient elements (Ca, Fe, K, Mg, Mn, P, S, and Zn) in the digested samples was determined using an inductively coupled plasma emission spectrometer (ICPE-9000, Shimadzu, Tokyo, Japan), according to the manufacturer’s instructions. At the end of the experiments, a precipitate (residue) formed in the pots, which in previous studies with peas and PGPR was collected and analyzed and contained precipitated Al [36 (link)]. In this work, the amount of Al in this residue was calculated as the difference between the amount of Al introduced into the pot and its total amount in the plants and the solution.