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Termites can create structures that alter the physical and chemical properties of soils. In this process, termites are selective about the soil constituents they will use to construct their mounds. Considering the common occurrence of termite mounds in Brazilian soils, this study aimed to investigate the selective action of termites in the mound building process. Samples were collected from six termite mounds and control soils (at a distance of 15 to 30 m from the termite mound) in different regions in Brazil to analyze the fine earth fraction. The content of clay fraction, organic C and Fe in pedogenic iron oxides increased in the mounds resulting in specific surface area increments. X-ray diffraction indicated a selectivity of termites by clay-sized particles such as kaolinite, gibbsite and iron oxides (hematite and goethite) rather than larger particles such as quartz. The proportion of low-crystalline iron oxides and the maghemite amount decreased in the mounds. The change of color parameters in the termite mounds was due to a combination of increase in clay fraction, organic carbon and iron oxides. The techniques used were sensitive, indicating changes and similarities between the control soils and the termite mounds.

Made available in DSpace on 2018-11-26T17:48:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-01-01. Added 1 bitstream(s) on 2019-10-09T18:27:24Z : No. of bitstreams: 1 S0100-06832018000100514.pdf: 290304 bytes, checksum: 0ff8739ab4a154929cbb4d4f969361e3 (MD5) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) There is a complex interaction between various components of the soil ecosystem, including microbial biomass and soil chemical contaminants such as heavy metals and radionuclides, which may greatly affect the efficiency of bioremediation techniques. The aim of this study was to investigate microbial capacity to change pH, changes in the metal soluble-exchangeable fraction, and effects of initial heavy metal contents on soil samples in microbial solubilization/immobilization capacity. The soil samples used in this study were collected at a known metal-contaminated site. Three highly metal-resistant bacteria were isolated from rhizosphere soil samples collected on weed species identified as Senecio brasiliensis, Senecio leptolobus, and Baccharis trimera. A completely randomized experimental design in a factorial arrangement was used, with three replicates. In general, with an acid pH, the isolates neutralized the contaminated growth media. In a neutral or basic initial pH, increases in pH were observed in the media, so these bacteria have an alkalizing effect on the growth media. Soluble metal contents were quite different and depend on the microbial species and heavy metal contents in the soil samples. The soluble-exchangeable fraction of metal such as Cu, Zn, Ni, Cr, Cd, Pb, and Ba may be unavailable after inoculation with heavy metal resistant rhizobacteria. A promising approach seems to be the application of inoculants with metal-resistant bacteria in bioremediation of multi-metal-polluted environments to improve the efficiency of this environmentally friendly technology. Univ Fed Piaui, Campus Cinobelina Elvas, Bom Jesus, Piaui, Brazil Univ Fed Rio Grande do Sul, Dept Solos, Porto Alegre, RS, Brazil Univ Estadual Paulista, Inst Biociencias Rio Claro, Programa Posgrad Ciencias Biol, Rio Claro, SP, Brazil Univ Fed Piaui, Programa Posgrad Solos & Nutr Plantas, Campus Cinobelina Elvas, Bom Jesus, Piaui, Brazil Inst Rio Grandense Arroz, Porto Alegre, RS, Brazil Univ Estadual Paulista, Inst Biociencias Rio Claro, Programa Posgrad Ciencias Biol, Rio Claro, SP, Brazil

O presente trabalho teve como objetivos avaliar a quantidade de nitrogênio imobilizado e a sua remineralização, nos sistemas plantio direto (SPD) e convencional (SC), ao longo do ciclo do milho. Para tal, foram coletadas amostras da camada de 0-5cm de solo semeado com milho em sucessão à aveia preta, sob os sistemas convencional e plantio direto, no dia da semeadura do milho e 46, 62, 88 e 112 dias após. Amostras da parte aérea das plantas de milho foram coletadas nas mesmas épocas, com exceção da primeira, e avaliadas quanto à quantidade de nitrogênio acumulado. As amostras de solo foram avaliadas quanto à quantidade de nitrogênio mineral no solo, de nitrogênio e carbono potencialmente mineralizáveis, atividade de urease e de nitrogênio imobilizado na biomassa microbiana. A imobilização microbiana do nitrogênio foi maior no sistema plantio direto, levando a uma menor quantidade de nitrogênio mineral no solo e resultando em menor acúmulo de nitrogênio na parte aérea do milho ao final do seu ciclo neste sistema, em comparação com o convencional. Não foi observada remineralização do nitrogênio imobilizado, indicando que a biomassa microbiana atuou mais como agente da mineralização de nitrogênio orgânico do que como fonte de nitrogênio potencialmente mineralizável. The present research aimed to evaluate the amount of nitrogen immobilized and its remineralization, in conventional and in no-till systems, during the corn cycle. A soil that was used for oats crop was seeded with corn and subjected to under conventional and no-till systems. Samples were collected from the top (0-5cm) soil layer on the day of the corn seeding and after 46, 62, 88 and 112 days. At the same time, the aerial parts of corn plants were collected and nitrogen accumulation was evaluated. Soil samples were assayed for mineral N, potentially mineralizable N and C, activity and immobilized N. Microbial nitrogen immobilization was higher in no-till system, reducing the soil mineral nitrogen concentration and resulting in a lower amount of nitrogen in the aerial parts of corn plants at the end of the growth cycle. Nitrogen remineralization was not observed, indicating that the microbial biomass acted more as an agent of organic N mineralization than as a source of potentially mineralizable N.