Formation and disappearance of phytotoxic Al tridecamer (Al13) in the rhizosphere can be affected by root exudates such as organic ligands. We investigated the effects of organic ligands on the formation and disappearance of Alla as a function of pH and COOH / Al ratio. The aqueous Al species were analyzed by using a liquid state27Al-NMR and an atomic absorption spectrometer and separated into four fractions, as follows; 1) Al13, 2) Al monomer and dimer (AlSYM), 3) Al complexed with organic ligands (AlORG), and 4) other undefined species (AlNON). Formation of Al13 was suppressed by acetate, oxalate, and citrate. In addition, Al13 that preexisted in a hydroxyaluminmn solution was disappeared by the introduction of acetate, oxalate, and citrate. Decrease in the concentration of Al13 at the early stage of the reaction was caused by the decomposition of Al13 along with the increase in the concentrations of AlSYM and AlORG. After 7 d of reaction, it was likely that Al13 was transformed into Al(OH)30 and other undefined species that could not be detected by27Al-NMR. The ability of the carboxylic groups to suppress the occurrence of Al13 (molar-basis) was in the order of acetate << oxalate < citrate, corresponding to the ability of complexation with Al. In conclusion, the phytotoxic effects of Al13 were less pronounced because of the ubiquitous presence of organic ligands in the rhizosphere.
All Science Journal Classification (ASJC) codes
- Soil Science
- Plant Science