Phosphorus applied to the root half without Al³⁺ exposure can alleviate Al toxicity on the other root half of the same <i>eucalyptus</i> seedling

Approximately 30% of the world’s land area is acidic soil (pH &lt; 5.5), and aluminum (Al) toxicity and phosphorus (P) deficiency are two main constraints of plant growth in acidic soil. However, direct application of P fertilizer to acidic soil can form insoluble Al–P precipitates, thus reducing P availability. We used a split-root technique to experimentally investigate whether <i>Eucalyptus</i> seedlings can translocate P from root halves with no Al stress to root halves experiencing Al stress, thus ameliorating the Al toxicity of the latter. The results revealed that P application led to fixation of Al in the form of an Al–P precipitate in sand, thus relieving Al toxicity. In addition, the application of P increased the nutritive P supply and alleviated P deficiency within the plant. In <i>Eucalyptus</i> seedlings, increased P application to the root half without Al³⁺ exposure alleviated Al toxicity in the other root half. The extent of resistance to Al stress depended on the genotype of the <i>Eucalyptus</i> seedlings. Based on our findings, P can be applied to areas not only through roots, but also by other methods, such as leaf fertilization or application of nutrient solutions to the trunk, preferably avoiding the formation of Al–P precipitates in the soil.