tese
Fungos micorrízicos arbusculares no crescimento, extração de metais e características anatômicas da Brachiaria decumbens Stapf em solo contaminado por metais pesados
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UNIVERSIDADE FEDERAL DE LAVRAS
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A intensificação da urbanização e das atividades industriais e agrícolas tem causado grande expansão das áreas contaminadas com metais pesados e conseqüências adversas ao meio ambiente, havendo necessidade de desenvolver tecnologias eficazes para remediação destas áreas. Uma tecnologia promissora é a fitorremediação, que consiste na utilização de plantas e sua microbiota associada para degradar ou remover matérias tóxicos do solo. Entretanto, os estudos desta técnica não tem dado a atenção devida aos microrganismos do solo, em especial aos fungos micorrízicos arbusculares (FMAs) que exercem efeito protetor para as plantas e facilitam absorção de íons da solução do solo. No presente trabalho avaliou-se a influência de diferentes FMAs no crescimento e na capacidade da Brachiaria decumbens de extrair Cd, Zn, Pb e Cu de um solo contaminado, bem como a influência destes fungos e da contaminação sobre as características anatômicas desta planta. Para isto realizaram-se dois experimentos em potes de plástico em casa de vegetação com mistura de solo contaminado contendo em mg kg-1: Zn=3.300; Cu=60; Cd=29 e Pb=73 (extração Mehlich-1), onde plantou-se Brachiaria decumbens inoculada ou não com 14 isolados de FMAs. Constatou-se que este nível de contaminação exerce efeito tóxico acentuado para a B. decumbens e que este efeito é amenizado pela inoculação com certos FMAs. O efeito protetor da simbiose é associado à redução da absorção ou translocação dos metais das raízes para a parte aérea, sendo efeitos diferenciados para os 14 isolados estudados. A inoculação causou aumento médio na produção de matéria seca de 84% em relação às plantas não inoculadas. Mesmo havendo redução na absorção de alguns metais, plantas micorrizadas aumentaram a quantidade de metais extraídos pela B. decumbens. Estes aumentos foram: 845, 142, 68 e 54% para Cu, Pb, Zn e Cd, respectivamente. Os efeitos na extração foram mais consistentes para o Cu. Apenas A. spinosa, A. morrowiae-UFLA e G. gigantea foram capazes de aumentar a extração dos quatro metais estudados. Estes efeitos dos FMAs aumentam o potencial fitorremediador da B. decumbens em solo tropical contaminado. Na segunda parte deste estudo avaliaram-se os efeitos da contaminação e da inoculação com FMAs selecionados sobre características anatômicas da planta. Verificou-se acentuada modificação nas folhas destacando-se redução no tamanho dos vasos e no número de células do parênquima foliar em conseqüência da elevada absorção dos metais. Este efeito foi de baixa intensidade nas plantas colonizadas por isolados que exerceram efeito protetor à planta. Houve também alterações na anatomia das raízes destacando-se redução na espessura e a área proporcional do córtex e do cilindro central e aumento na epiderme, exoderme e parênquima lignificado. Em raízes de plantas colonizadas com S. pellucida verificou-se alterações nos encaixes celulares da exoderme, endoderme, havendo encaixes tipo braciforme. Conclui-se que os efeitos dos FMAs na proteção e acúmulo de metais pesados na B. decumbens difere de modo acentuado. Estes efeitos são mais acentuados e consistentes para S. pellucida e A. morrowiae, sendo esses resultantes da maior retenção, principalmente do Cu nas raízes. Fica demonstrado o potencial desta simbiose para a fitorremediação de solos contaminados com metais pesados.
Intensification of urbanization and industrial and agricultural activities has caused great expansion of heavy metal contaminated areas, thereby having adverse environmental consequences, evidencing the need to developing efficient technology for remediating these areas. One promising technology is phytorremediation, which consists of utilizing plants and their associated microbiota to degrade or to remove toxic material from soil. However studies of technique have given the deserved attention to soil microorganisms, mainly arbuscular mycorrhizal fungi (AMF) that exhibit plant protection and facilitate ionic absorption from soil solution. In the present study influence of deferent AMF on growth and total extraction of Cd, Zn, Pb and Cu from a contaminated by Brachiaria decumbens, as well as contamination and fungal effects on plant anatomical characteristics were evaluated. Two experiments were conducted under greenhouse conditions in plastic pots with a soil mix containing in mg kg-1: Zn= 3300, Pb= 73, Cu= 60 and Cd= 29 (Mehlich 1). Soil was planted with Brachiaria decumbens inoculated with 14 differents AMF. It was found that contamination markedly inhibits plant growth being much effect a consequence of high metal uptake and shoot translocation. Contamination inhibition was verified by inoculation with certain AMF isolates. The symbiosis protecting effect was related to a reduction in metal uptake by roots or translocation to shoots. Such effect was highly influenced by the fungal isolates. The average effect of inoculation on dry matter yield was 84%, over non-mycorrhizal controls. Even with the reduction in metal uptake, mycorrhizal plants accumulated more metal than non-mycorrhizal ones. Such increase in metal accumulation was: 845, 142, 68 and 54% for Cu, Pb, Zn and Pb, respectively. Effects on extraction were more consistent for Cu than for any other metal. Only three isolates A. spinosa, A. morrowiae-UFLA and G. gigantea increased total accumulation of all four metals studied. AMF benefits to metal accumulation enhance the phytorremediation potential of Brachiaria decumbens in contaminated tropical soils. In a second part of this study effects of contamination and inoculation with selected AMF on anatomical characteristics of Brachiaria decumbens were investigated. Marked anatomical modification caused by contamination was found in leaf tissues. There was a reduction in vessel size and in the cell density in the foliar parenchyma. These effects happened at a much lower intensity in plants colonized by AMF that also exhibit protection effects on plant growth. Root anatomy was also affected by contamination: reduction in cortical tissue, in the central cylinder and an increase in epiderm, exoderm and lignified parenchyma. In roots colonized by S. pellucida it was found alterations in exodermal and endodermal cell shapes. These cells exhibits lateral projections that facilitate cell junctions. As conclusions, the protecting effects of AM and heavy metals accumulation by Brachiaria decumbens differ quite substantially. Such effects were more pronounced in plants colonized by S. pellucida and A. morrowiae, which were capable to retain metal mainly in the roots. The potential of this symbiosis to phytorremediation of heavy metal contaminated soil was demonstrated.
Intensification of urbanization and industrial and agricultural activities has caused great expansion of heavy metal contaminated areas, thereby having adverse environmental consequences, evidencing the need to developing efficient technology for remediating these areas. One promising technology is phytorremediation, which consists of utilizing plants and their associated microbiota to degrade or to remove toxic material from soil. However studies of technique have given the deserved attention to soil microorganisms, mainly arbuscular mycorrhizal fungi (AMF) that exhibit plant protection and facilitate ionic absorption from soil solution. In the present study influence of deferent AMF on growth and total extraction of Cd, Zn, Pb and Cu from a contaminated by Brachiaria decumbens, as well as contamination and fungal effects on plant anatomical characteristics were evaluated. Two experiments were conducted under greenhouse conditions in plastic pots with a soil mix containing in mg kg-1: Zn= 3300, Pb= 73, Cu= 60 and Cd= 29 (Mehlich 1). Soil was planted with Brachiaria decumbens inoculated with 14 differents AMF. It was found that contamination markedly inhibits plant growth being much effect a consequence of high metal uptake and shoot translocation. Contamination inhibition was verified by inoculation with certain AMF isolates. The symbiosis protecting effect was related to a reduction in metal uptake by roots or translocation to shoots. Such effect was highly influenced by the fungal isolates. The average effect of inoculation on dry matter yield was 84%, over non-mycorrhizal controls. Even with the reduction in metal uptake, mycorrhizal plants accumulated more metal than non-mycorrhizal ones. Such increase in metal accumulation was: 845, 142, 68 and 54% for Cu, Pb, Zn and Pb, respectively. Effects on extraction were more consistent for Cu than for any other metal. Only three isolates A. spinosa, A. morrowiae-UFLA and G. gigantea increased total accumulation of all four metals studied. AMF benefits to metal accumulation enhance the phytorremediation potential of Brachiaria decumbens in contaminated tropical soils. In a second part of this study effects of contamination and inoculation with selected AMF on anatomical characteristics of Brachiaria decumbens were investigated. Marked anatomical modification caused by contamination was found in leaf tissues. There was a reduction in vessel size and in the cell density in the foliar parenchyma. These effects happened at a much lower intensity in plants colonized by AMF that also exhibit protection effects on plant growth. Root anatomy was also affected by contamination: reduction in cortical tissue, in the central cylinder and an increase in epiderm, exoderm and lignified parenchyma. In roots colonized by S. pellucida it was found alterations in exodermal and endodermal cell shapes. These cells exhibits lateral projections that facilitate cell junctions. As conclusions, the protecting effects of AM and heavy metals accumulation by Brachiaria decumbens differ quite substantially. Such effects were more pronounced in plants colonized by S. pellucida and A. morrowiae, which were capable to retain metal mainly in the roots. The potential of this symbiosis to phytorremediation of heavy metal contaminated soil was demonstrated.
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SILVA, S. da. Fungos micorrízicos arbusculares no crescimento, extração de metais pesados e características anatômicas da Brachiaria decumbens Stapf. em solo contaminado. 2006. 80 p. Tese (Doutorado em Ciência do Solo)-Universidade Federal de Lavras, Lavras, 2006.