Apparent phytotoxicity of mononuclear hydroxy-aluminum to four dicotyledonous species |
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Authors: | Thomas B. Kinraide David R. Parker |
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Affiliation: | Appalachian Soil and Water Conservation Res. Lab., ARS, USDA, Beckley, WV 25802-0867, USA;Dept of Soil and Environmental Sciences, Univ. of Calif., Riverside, CA 92521-0424, USA |
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Abstract: | It has long been assumed that Al3+ is an important rhizotoxic ion in acid soils around the world, but the toxicity of Al3+ relative to mononuclear hydroxy-Al [AlOH2+ and Al(OH)+2] has been examined in detail only for an Al-sensitive wheat variety ( Triticum aestivum L. cv. Tyler). That plant appears to be sensitive to Al3+ but not to AlOH2+ and Al(OH)+2. New experiments, and reanalyses of previously published experiments, provide evidence that dicotyledonous species may be sensitive to mononuclear hydroxy-Al and that Al3+ may be nontoxic, or less toxic, to those plants. Despite these consistently measured differences between wheat and the dicotyledons, the determination of relative toxicities (Al3+ vs mononuclear hydroxy-Al) may be an intractable problem. Because of hydrolysis equilibria, (AlOH2+) and (Al(OH)+2) are equivalent to (Al3+)k1(H+)−1 and (l3+)k2(H+)−2, respectively, in which k1 and k2 are the first and second hydrolysis constants (braces denote activities). Thus, any expression of root elongation as a function of mononuclear hydroxy-Al can be alternatively expressed as a function of (Al3+) and (H+). Toxicity attributed to mononuclear hydroxy-Al may actually be Al3+ toxicity that increases as pH rises (i.e. Al3+ toxicity ameliorated by H+). |
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Keywords: | Aluminum Brassica campestris Glycine max hydroxy-aluminum Lactuca sativa roots toxicity Trifolium pratense |
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