MECHANISM OF SILICON INDUCED ALLEVIATION OF ALUMINUM PHYTOTOXICITY

Complexation of aluminum (Al) with silicon (Si) has been attributed as a mechanism of Si induced alleviation of Al toxicity to plants. Effec ts of various concentrations of Si (0, 534, 1068, or 1602 mu M) on roo t growth of two sorghum cultivar seedlings (NB9040 and Martin) was eva luated in nutrient solutions containing 0 or 296 mu M Al. Three experi ments were conducted with variation in the sequence of pH adjustment o f the solution, and addition of Al and Si stock solutions. In solution s containing 296 mu M Al with no Si, growth of sorghum seedlings was s ignificantly decreased as compared to that of the seedlings grown in s olutions containing 0 Al. Root growth of seedlings of both cultivars i n solutions containing 296 mu M Al improved significantly with increas ing concentrations of Si, but only when Al was added to the basal nutr ient solution following the addition of Si without lowering the soluti on pH. Addition of Si to the basal nutrient solution increased the pH greater than or equal to 10.0, which facilitated precipitation of Al, thus decreasing its toxicity. If the solution pH was lowered to 4.0 fo llowing the addition of Si, prior to the addition of Al, the toxicity of Al was least influenced by the presence of Si in solution within th e range of 534 to 1602 mu M. Silicon-induced alleviation of Al toxicit y appears to be due to pH effects and not the direct effects of Si on Al in solutions.