EFFECTS OF PHOSPHORUS ALUMINUM MOLAR RATIO AND CALCIUM-CONCENTRATION ON PLANT-RESPONSE TO ALUMINUM TOXICITY

Total aluminum (Al) in solution often comprises both monomeric and polymeric Al species. Concentrations of total and monomeric Al and SIGMA activities of monomeric Al species ( SIGMA a(Al mono)) were determined in nutrient solutions at 40 mu M Al with varying P/Al molar ratios (0, 0. 02, 0. 2, 2. 0 and 4. 0) and calcium (Ca) concentrations (0. 5, 1. 5, 5. 0, 15 mM). Effects of these treatments on root elongation of soybean left bracket Glycine max(L. ) Merr. right bracket , sunflower (Helianthus annuus L. ), subterranean clover (Trifolium subterraneum L. ), and alfalfa (Medicago sativa L. ) were determined. Concentrations of total and monomeric Al in solution decreased with increasing P/Al molar ratio. Ca concentration had no significant effect on concentration of total or monomeric Al, but significantly affected the SIGMA a(Al mono) in solution. Root elongation of the plant species increased with increasing P/Al molar ratio and Ca concentration.