In Rio Grande do Sul the potato (Solanum tuberosum L.) can be grown in fall and spring. However, due to the contrasting weather conditions between these two seasons, which directly influence the growth of plants and the formation of tubers, it is necessary to identify potato clones adapted to such growing conditions. Thus, this work was carried out to characterize the efficiency of P use in potato clones grown in two contrasting seasons, in an off-soil growing system using sand as a substrate. The treatments were combined in a 2 x 4 x 2 factorial, consisting of two levels of P in the nutrient solution (2.32 and 23.2 mg P L-1), four potato clones (Asterix, Atlantic, SMIC 148-A and SMINIA 793101-3) and two growing seasons (spring and fall). The number of leaves and tubers per plant, the fresh and dry mass of the tubers, fresh mass of the shoot, P concentration in shoot and tubers, and efficiency of P use were determined. There is a difference between the potato clones in terms of the efficiency of P use in the spring and autumn crops of Rio Grande do Sul. Asterix and SMINIA 793101-3 clones show higher productivity in the spring growing and without P. restriction. SMIC 148-A clone was not influenced by the growing season, as long as the availability of P is not a limiting factor. Atlantic clone shows good production when grown in the fall, regardless of the level of P used

The aim of this work was to evaluate the effect of different concentrations of aluminum (Al) on physiological and biochemical parameters of Luehea divaricata seedlings grown in a hydroponic system under greenhouse conditions to verify the possible tolerance to Al or phytoremediation potential of this species. Seeds of Luehea divaricata were placed to germinate in commercial substrate and after 30 days the seedlings were transferred to a hydroponic system with a complete nutrient solution, pH at 4.5±0.1, with daily adjustment. After 20 days of acclimatization, homogenous plants were selected and transferred to a new nutrient solution (without phosphorus (P) and pH at 4.5±0.1) with different concentrations of Al: 0, 25, 50, 75 and 100 mg L -1 , each treatment being composed of 10 replicates of one plant each. The experiment was conducted in a completely randomized design. After seven days of exposure to the treatments, plants were collected for physiological and biochemical analyzes. Aluminum promoted a significant reduction in fresh and dry weight of roots, stems and leaves; in plant height; leaf number; leaf area; and pigment content. On the other hand, Al promoted an increase in lipid peroxidation and guaiacol peroxidase enzyme activity. Therefore, the presence of Al in the growth medium, for the studied conditions, altered significantly both physiological and biochemical parameters in Luehea divaricata seedlings, presenting a sensitive behavior to this element. Due to these characteristics, the studied species does not show phytoremediation potential.

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