Manganese (Mn) is an essential micronutrient for plants, however in high concentrations it becomes phytotoxic. Some soils may have, in addition to high amounts of aluminium and low pH, high amounts of Mn. In addition, Mn becomes more available at low pH. Thus, the goal of the present work will be to evaluate the effects of Mn excess on germination and initial growth of two native species of tree legumes of the subfamily Mimosoideae: one species characteristic of Cerrado, Stryphnodendron adstringens (barbatimão) and another characteristic of the Atlantic Forest, Mimosa bimucronata (maricá). Our hypothesis is that Mn in high concentrations in the soil with low pH will promote toxic effects on the germination and growth of these species. To test this hypothesis, seeds of these species will be germinated directly in 3-liter pots in soil with different concentrations of Mn (0, 150, 300, 600 mg. Kg-1). After germination, only one seedling will be kept per pot. After 90 days of germination, plants will be collected and growth analysis will be carried out, including fresh and dry biomass of shoot (stem and leaves) and root, leaf area and related aspects to nodulation. Mycorrhizal colonization of the roots will also be evaluated. Photosynthetic pigments, as well as compounds related to nitrogen metabolism and plant stresses, such as malondialdehyde (MDA - TBARs), nitrate, ammonia, and total amino acids, will be measured. Based on the methodology used, it is expected to observe possible changes in growth and in the physiology of these plants under excess of Mn. It is also expected that the plants have different mechanisms of susceptibility and/or tolerance to Mn and that arbuscular mycorrhizal fungi (AMFs) can assist in this tolerance.
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