Unveiling the aluminum tolerance by Tithonia diversifolia grown in acid soil: Insights from morphological, anatomical, and nutritional analysis

Acidic soils cover two-thirds of Brazil's land, significantly reducing pasture productivity and resilience. Tithonia diversifolia has emerged as a promising forage alternative for such soils. The objective of this study was to assess the effect of different soil acidity levels, determined by base-cation saturation (BCS) levels, on the anatomical, and morphological analyses of the roots, the nutritional status of the plants, as well as the root and shoot biomass production. A 107-days greenhouse experiment was carried out, employing a randomized block design with a 2 x 4 factorial arrangement. The factors included two propagation methods (seeds and stem cuttings) and four BCS levels (19%, 39%, 52%, and 63%). There was no observed interaction between propagation methods and BCS levels regarding root and shoot biomass production. This indicates that T. diversifolia's tolerance to acidic soils is not affected by the propagation method. However, stem-propagated plants exhibited significantly greater root (31% increase) and shoot (26% increase) biomass production compared to seed-propagated plants. Regardless of the propagation method, T. diversifolia plants grown in soil with a 19% BCS level showed a substantial reduction in root (45% decrease) and shoot (31% decrease) biomass compared to the 63% BCS level treatment. The root anatomy and morphology of T. diversifolia are affected when cultivated in acidic soils with a 19% BCS level. Nevertheless, the Periodic Acid Schiff (PAS) test detected some mucilage in T. diversifolia roots, suggesting a potential defense mechanism for Al3+. The shoot biomass of T. diversifolia plants cultivated in soil with a 19% BCS level exhibited greater nutritional values compared to the 63% BCS level. In conclusion, propagation methods have a limited impact on the tolerance of T. diversifolia to acidic soils. Despite the negative effects on root and shoot biomass production, T. diversifolia effectively maintains nutrient uptake even under acidic soil conditions with Al3+ availability of 5 mmol(c) dm(-3).