Evaluation of mycorrhizal influence on the development and phytoremediation potential of Canavalia gladiata in Pb-contaminated soils.

Soil contamination by heavy metals is a serious problem to humans due to its high level of toxicity. The heavy metal lead (Pb) is commonly used in industries and if the disposal of residues that contain this element is not done properly may result in tragic consequences to the organisms. In this experiment we assessed the potential of a forrage leguminous, Canavalia gladiata, to phytoremediate lead-contaminated soil under mycorrhizal influence. The experimental design was composed of 4 Pb doses (0, 250, 500, and 1000 mg kg(-1) of soil) and the plants were inoculated or uninoculated with arbuscular mycorrhizal fungi (AMF). We observed that the nodulation was severely affected by the presence of Pb independently of the mycorrhizal status; most of the elements analyzed were affected independently of the mycorrhizal status with exception of P. The mycorrhizal colonization was able to restrict the entrance of Pb in plants under high concentrations of Pb but promoted it's accumulation in both organs under intermediate concentrations of this element. Besides the mycorrhization did not promote plant growth under Pb stress, the use of this plant may be considered to be used for phytostabilization purposes.

Lead tolerance and phytoremediation potential of Brazilian leguminous tree species at the seedling stage.

A greenhouse pot experiment was conducted to evaluate the potential of three Brazilian leguminous woody species, Mimosa caesalpiniaefolia, Erythrina speciosa and Schizolobium parahyba, for the revegetation of lead- (Pb-) contaminated areas. The response of seedlings to increasing Pb concentrations (0, 250, 500 and 1000 mg kg(-1)) in the soil was studied. In addition to Pb accumulation and translocation, the following parameters were assessed: chlorophyll, nitrate, ammonia, lipid peroxidation (MDA) and free amino acid content; seedling growth; and nitrogenase activity. No differences were observed in the germination of woody species seeds sown in soils with or without Pb addition. M. caesalpiniaefolia did not show visual symptoms of Pb toxicity, while the other two species demonstrated stress symptoms, including reduced shoot biomass yield, leaf area and height. Biochemical analyses of plant tissues revealed markedly different responses to increasing Pb concentrations, such as changes in foliar soluble amino acid composition in S. parahyba; changes in ammonia and nitrate content in E. speciosa, M. caesalpiniaefolia and S. parahyba; and changes in MDA content in S. parahyba. The levels of chlorophyll a and b and carotenoid were affected in the species studied. For the Nitrogen-fixing (N(2)-fixing) species E. speciosa, an increase of Pb in the soil affected nodule formation and growth, which led to reduced nitrogenase activity in seedlings. The concentration of Pb in shoots and roots increased with the Pb concentration in soil. However, most of the Pb absorbed accumulated in the roots, and only a small fraction was translocated to aboveground parts. These findings were confirmed by the low bioconcentration factor (BCF) and translocation factor (TF) values for the three species. The tolerance index (TI) values suggested that M. caesalpiniaefolia, a N(2)-fixing tree, was the species that was most tolerant to high Pb concentrations in soil, while E. speciosa and S. parahyba showed moderate tolerance. Of the three Brazilian native woody species studied, M. caesalpiniaefolia was found to have the highest Pb tolerance and phytostabilisation potential in Pb-contaminated soils.

Growth of Crotalaria juncea L. supplied with mineral nitrogen

Plantas de Crotalaria juncea inoculadas com Rhizobium foram tratadas com solução nutritiva contendo 10 ou 20mg de N/NO3 ou N/NH4.planta-1 .semana-1. As plantas controle receberam solução nutritiva sem N. Foi verificado o efeito destas fontes de N no crescimento e fixação de nitrogênio em plantas com 30, 60 e 90 dias após a semeadura (DAS). Aquelas que receberam N mineral apresentaram maior crescimento que plantas -N, mas a presença de nódulos ocorreu em todos os tratamentos. Plantas tratadas com NH4 apresentaram maior conteúdo de N até os 60 dias. As maiores concentrações de leghemoglobina e proteínas em nódulos foram verificadas aos 30 DAS e não houve diferença no conteúdo de leghemoglobina entre os tratamentos, em nenhuma das idades e em proteínas a partir de 60 DAS. A atividade da nitrogenase não variou dos 60 aos 90 dias, com exceção de plantas que receberam 20mg N/NO3, nas quais esta foi maior aos 60 dias.