Physiological, anatomical and ultrastructural effects of aluminum on Styrax camporum, a native Cerrado woody species.

Styrax camporum Pohl. (Styracaceae) is a woody species that grows on acidic soils from the Brazilian savanna with high aluminum (Al) saturation (m% > 50%), where it accumulates ~ 1500 mg Al per kg dry leaves. Using nutrient solution, a previous study showed that 1480 µM Al causes toxicity symptoms, which raises the question whether less than 1480 µM Al could cause beneficial effects on this species. Here, we checked possible altered gas exchange rates, damage to organelles in root tips and the association between Al exposure and mitochondria occurrence in cells of root tips, once organic acids from Krebs cycle exuded by the roots of this species when exposed to Al have been recently evidenced. Five-month-old plants were grown in nutrient solution with 0, 740 and 1480 µM Al for 90 days. Plants exposed to 1480 µM Al showed less developed root system, reduced plant height and low gas exchange rates in relation to those exposed to 0 and 740 µM Al, confirming that 1480 µM Al is toxic to S. camporum. However, plants exposed to 0 and 740 µM Al had similar number of leaves, plant height, root biomass, root length, total plant biomass and gas exchange rates, indicating that no beneficial effects from 740 µM Al could be noted on this species. In plants exposed to 0 and 740 µM Al, mitochondria were noted at the root tip, while at 1480 µM Al these organelles were not evident due to the conspicuous vacuolation of root cells. S. camporum shows limited tolerance to Al in nutrient solution. In addition, this species is not dependent on Al to grow and develop because the plants grew well under 0 and 740 µM Al.

Root, shoot and leaf traits of the congeneric Styrax species may explain their distribution patterns in the cerrado sensu lato areas in Brazil.

Shoot and root lengths, the number of leaves, biomass and leaf area were measured in Styrax ferrugineus Nees and Mart., Styrax camporum Pohl. and Styrax pohlii A. DC cultivated in rhizotrons. Additionally, young individuals of these species were planted in a cerrado sensu stricto (s. str.), at the edge and in the understorey of a cerradão, and in the understorey of a riparian forest. Six months after planting, the specific leaf area (SLA) and the CO2 assimilation rate were assessed on an area (Aarea) and mass (Amass) basis. S. ferrugineus exhibited greater root and lower shoot length in comparison to S. pohlii. The high shoot growth and concomitantly substantial root length of S. camporum may illustrate why this species is widely distributed in the cerrado sensu lato areas, whereas the deep roots of S. ferrugineus could account for its occurrence in the cerrado s. str. In the field, an irradiance-diminishing gradient enlarged the SLA of S. pohlii, which positively influenced its Amass, and which could partially explain its occurrence in shady habitats. However, a non-plastic trait, such as the high shoot length of S. pohlii, is more likely to be responsible for the success of this species in forest habitats.