Aluminum toxicity and speciation in soil liquids—experiments with Allium cepa L

Allium cepa L. was grown in soil liquids from beech, birch, and spruce stands of south Sweden. Root growth, cytology, and morphology at different concentrations and speciation of aluminum were studied. A strong cation exchange resin was used to discriminate between toxic and nontoxic species of Al. Root growth was inhibited in all soil liquids compared to controls and was nonlinearly related to the total Al concentration. Cytological changes (i.e., release of nucleolar material into the cytoplasm) were found in certain root tip cells and appeared over the whole Al concentration range of the soil liquids studied. The ion exchange method investigated was able to discriminate between toxic and nontoxic Al in the soil liquid from the mor layer of a podzol (dissolved organic carbon content = 80 mg/L). Labile Al, predominantly corresponding to inorganic monomeric Al forms, made up the toxic Al fraction.