Buffered,phosphate-containing media suitable for aluminum toxicity studies |
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Authors: | Kinraide Thomas B Sweeney Billie K |
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Institution: | (1) Appalachian Farming Systems Research Center, Agricultural Research Service, United States Department of Agriculture, Beaver, West Virginia 25813-9423, USA |
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Abstract: | Studies of Al rhizotoxicity sometimes require the use of well-defined rooting media. For that reason, buffers and phosphate are often omitted from Al solutions for which species composition must be determined precisely. Homopipes and succinate appear to be suitable buffers for short-term studies with seedlings of an Al-sensitive wheat (Triticum aestivum L. cv. Scout 66) and white clover (Trifoliau repens L. cv. Huia). In the case of homopipes (homopiperazine-N,N -bis-2-ethane-sulfonic acid]), a slight inhibition of root elongation must be taken into account, but no binding of Al3+ was observed. In the case of succinate, no inhibition of root elongation was observed, but Al3+ binding must be considered. Phosphate-containing media remain free of solid-phase or polynuclear species whenever {Al3+}2{HPO4
2-}{OH–}3 < 10–47.0 (or {Al3+}{HPO4
2-}{OH–}< 10–22.7) and when {Al3+}3 / {H+}3 < 108.8. These ion activity products, that define stable Al solutions in the laboratory, appear to apply in soils also, according to an analysis of published data. The published equilibrium values {AlH2PO4
2+} / ({Al3+}{H2PO4
–}) = 103.0, {AlHPO4
+} / ({Al3+}{HPO4
2-}) = 107.0, and {Alsuccinate+} / ({Al3+}{succinate 2-}) = 104.62 appear to be suitable, because solution toxicity could be accounted for entirely on the basis of computed Al3+ even in solutions containing high levels of Alsuccinate+ and AlHPO4
+ (in every case {AlHPO4
+}>> {AlH2PO4
2+}). Thus, AlHPO4
+ and Alsuccinate+ were not toxic at achieved concentrations. |
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Keywords: | aluminum buffer homopipes phosphate root succinic acid toxicity |
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