Toxicity of Aluminum to Coffee Seedlings Grown in Nutrient Solution

<jats:title>Abstract</jats:title> <jats:p> A solution culture experiment was conducted with coffee seedlings ( <jats:italic>Coffea arabica</jats:italic> L.) to determine the combined effect of ionic strength and aluminum (Al) concentration of nutrient solutions on Al availability. The treatments consisted of three Al concentrations: 0.0, 0.037, and 0.148 mmol dm <jats:sup>−3</jats:sup> . These were combined with five levels of ionic strength produced by diluting a complete nutrient solution to relative concentrations of 0.5, 0.25, 0.10, and 0.01. The phosphorus (P) concentration of each solution was adjusted to 0.1 mmol dm <jats:sup>−3</jats:sup> . The pH of the solutions was maintained at 4.0 ± 0.2. Shoot and root growth decreased progressively under the Al treatments. The lateral roots of Al‐stressed plants were thicker, shorter, and fewer in number than those of the control plants. The younger leaves of Al‐stressed plants were small, curled along the margins, and frequently chlorotic along the leaf margin. </jats:p> <jats:p> At a constant Al concentration, seedling growth was reduced with dilution of the nutrient solution. This decrease in growth was best correlated with an increase in the activity of Al <jats:sup>3+</jats:sup> . An Al <jats:sup>3+</jats:sup> activity value of 1.2 × 10 <jats:sup>−5</jats:sup> was associated with a 10% reduction of coffee seedling growth. </jats:p>