Impact of aluminum supply on the growth of seed-grown yerba mate (Ilex paraguariensis) seedlings

Aluminum (Al) has long been regarded as toxic to plants, but recent research suggests it may also play a beneficial role in plant nutrition. Yerba mate (Ilex paraguariensis) is known for naturally thriving in acidic and Al-rich soils. The objective of the present study was to evaluate the effect of supplying Al, with or without the addition of controlled-release mineral fertilization, on the growth of yerba mate seedlings obtained from seeds. The mineral fertilization of the substrate enhanced the growth, biomass production, and quality of the produced yerba mate seedlings. Al supply did not exhibit beneficial effects on the development of seed-propagated yerba mate seedlings, except for root fresh volume, which showed a positive response to moderate Al doses. The yerba mate seedlings had a high tolerance to the presence of Al in the substrate, withstanding monthly applications of up to 1,000 mg Al3+ per dm-3 of substrate without displaying toxicity symptoms. Nevertheless, higher Al doses caused severe toxicity in yerba mate seedlings, which was visibly manifested by the development of short, thick, and dark-colored roots. In the shoot of the seedlings, Al toxicity symptoms generally occurred indirectly, as evidenced by reduced growth and a decrease in dry matter production. However, in the most affected plants, dark spots were observed on the shoot, starting at the tips of the younger leaves and progressing across the entire leaf, ultimately causing leaf abscission and, subsequently, plant death.