F. M. S. Moreira

Eficiência e diversidade fenotípica de bactérias diazotróficas que nodulam caupi [Vigna unguiculata (L.) Walp] e feijoeiro (Phaseolus vulgaris L.) em solos de mineração de bauxita em reabilitação

A atividade de mineracao provoca degradacao ambiental em varias partes do mundo, e tecnicas de revegetacao, empregando diversas especies vegetais, tem sido indicadas, com vistas em reabilitar essas areas. A eficiencia e a diversidade de grupos-chave de bacterias, como as que nodulam leguminosas e fixam N2 (BNLFN), sao de extrema importância, uma vez que estas participam de processos de ciclagem de nutrientes e contribuem para a sustentabilidade dessas areas. Com o objetivo de avaliar a eficiencia e a diversidade de BNLFN, coletaram-se amostras de solo de areas mineradas, sob diferentes estrategias e cronossequencias de reabilitacao, no verao de 1999, para instalacao de ensaios, empregando feijoeiro e caupi como especies de plantas-isca de BNLFN. Na floracao, coletaram-se as plantas e avaliaram-se materia seca da parte aerea, numero, materia fresca e atividade de nodulos. Nao houve influencia das diferentes estrategias de reabilitacao na eficiencia das populacoes de BNLFN no crescimento do feijoeiro. A diversidade fenotipica dos isolados de BNLFN foi avaliada por meio das caracteristicas culturais destes em meio de cultivo 79. Apos a caracterizacao fenotipica de 328 isolados de feijoeiro e 420 de caupi, verificou-se que este e mais indicado que o feijoeiro nos estudos de nodulacao, eficiencia e diversidade de BNLFN. O impacto negativo da mineracao e maior na diversidade fenotipica cultural de BNLFN do que na nodulacao das plantas-isca utilizadas. A revegetacao contribuiu para aumentar a diversidade dessas bacterias em solos de areas de mineracao de bauxita, especialmente quando ocorreu a introducao de leguminosas.

DENSIDADE E DIVERSIDADE FENOTÍPICA DE BACTÉRIAS DIAZOTRÓFICAS ENDOFÍTICASEM SOLOS DE MINERAÇÃO DE BAUXITA, EM REABILITAÇÃO

Bacterias diazotroficas endofiticas contribuem para o desenvolvimento das plantas por meio da fixacao biologica do nitrogenio, producao e liberacao de substâncias reguladoras do crescimento vegetal, podendo, assim, facilitar a revegetacao de solos degradados por atividades antropicas. No entanto, pouco se conhece sobre as populacoes destas bacterias em solos ou plantas de areas de mineracao. Objetivando avaliar o efeito de diferentes tipos de vegetacao e tempo de reabilitacao de areas degradadas por mineracao de bauxita na densidade e diversidade de algumas especies de bacterias diazotroficas endofiticas, realizaram-se, em duas epocas, amostragens de solo, de dois ambientes distintos, submetidos a diferentes processos de reabilitacao. A densidade, avaliada pelo numero mais provavel, utilizando os meios de cultura: NFb, JNFb e Fam, para Azospirillum brasilense e A. lipoferum, Herbaspirillum spp. e A. amazonense, respectivamente, variou de 0 a 2,0 x 104 bacterias por grama de solo e mostrou que o tipo de vegetacao influiu nas populacoes destas bacterias. Foram encontradas densidades maiores em solos revegetados com gramineas: braquiaria (Brachiaria decumbens), capim-azevem (Lolium multiflorum) e capim-gordura (Melinis minutiflora). Contudo, estas densidades podem ser consideradas baixas, se comparadas as de solos agricolas, e nao apresentaram relacao com o tempo de reabilitacao da area. Foram encontrados 36 fenotipos culturais em meio batata, entre os 72 isolados obtidos dos tres meios de cultura utilizados. A partir destes, foram formados sete grandes grupos com similaridade superior ou igual a 63 %, dos quais cinco, representando 62,5 % do total de isolados obtidos, continham as estirpes-tipo de Burkholderia brasilensis, Herbaspirillum seropedicae e Azospirillum spp. (A. brasilense, A. amazonense, A. lipoferum, A. irakense). Apesar da baixa densidade, este grupo de bacterias apresentou alta diversidade fenotipica no ambiente estudado.

Efeito de ZN, Cd e Cu no comportamento de fungos ectomicorrízicos em meio de cultura

Ectomycorrhizal fungi are able to tolerate toxic heavy-metal concentrations in host plants, although being also negatively affected by excessive metal. Isolates of Pisolithus tinctorius and Scleroderma bovinus were grown for 20 days at 28°C in a liquid medium with increasing levels of Zn, Cu and Cd sulfates in 125 mL conical flasks containing 50 mL of MMN medium, adjusted to pH 4.8. Fungi growth was inhibited by heavy metal increasing concentration, which was different for fungi and metals. The 50% effective concentrations inhibiting growth were 2.71 x 10-3 mol L-1 of Zn, 1.18 x 10-3 mol L-1 of Cu and 12.2 x 10-6 mol L-1 of Cd to the P. tinctorius; and of 2.15 of Zn, 0.12 x 10-3 mol L-1 of Cu and 7.2 x 10-6 mol L-1 of Cd to the S. bovinus. The inhibiting heavy-metal effect on growth was in the following sequence: Cd > Cu > Zn. The fungus S. bovinus demonstrated Zn tolerance similar to P. tinctorius, being less tolerant to Cu and Cd. The growth of P. tinctorius was favored by addition of a low amount of Cu. Production of extracellular pigments by the two isolates was enhanced by the addition of all the heavy metals studied. The fungus P. tinctorius produced more pigments per gram of mycelia, suggesting that there was a positive relationship between pigment production capacity and heavy-metal tolerance.

Tolerância de fungos ectomicorrízicos a metais pesados em meio de cultura adicionado de solo contaminado

Ectomycorrhizal symbiosis can play a crucial role in protecting plant roots from heavy metals. However, a high heavy metal contamination can inhibit ectomycorrhizal fungi growth and activity, negatively influencing mycorhizal symbiosis. The growth of nine isolates of Pisolithus tinctorius, two of Suillus bovinus and one of Scleroderma sp. was assessed to evaluate the effect of Zn, Cd, Cu and Pb contaminated soil-sand mixes added to the liquid culture media, at different proportions. Addition of contaminated soil to the media reduced mycelial growth of all isolates, except of PT-306 at media with low proportion of contaminated soil mixes. The isolates showed inter and intra-specific variations in multiple contaminated soil. In general, Pisolithus isolates were more tolerant than those of S. bovinus or Scleroderma sp., with PT-306 being the most tolerant. S. bovinus isolates considered tolerant to Zn were sensitive to multiple soil contamination. Production of extracellular pigments by PT-306 and SB was enhanced by either addition of contaminated soil and a larger production of PT-306 pigments can be involved with its greater tolerance to heavy metals. PT-306 growth was favored by the addition of a low proportion of contaminated soil into the media. The addition of heavy metal contaminated soil into media was efficient to assess the impact of heavy metal multi contamination on ectomycorrhizal fungi.

Nodulação e crescimento de 49 leguminosas arbóreas nativas da Amazônia em viveiro

Although periodically flooded ecosystems represent 25% of the total Amazon area, they contribute to 75% of timber production. Both periodically flooded and upland ecosystems are greatly diverse in species belonging to Leguminosae family. Some of these species are currently exploited, but the economic potential of the vast majority has been overlooked. The knowledge of the plant growth characteristics of these species under nursery conditions is the first step to understand their biology and establish artificial woodlands in deforested areas. This paper reports data on the initial growth and nodulation of 49 species native from both Amazonian ecosystems. All experiments were carried out at the Instituto Nacional de Pesquisas da Amazonia, State of Amazonas, Brazil, during 1985 and 1986. Pre-germinated seedlings were transplanted into plastic bags containing five different substrata under nursery conditions. All species developed well and no differences amongst substrata were observed, except for a few species which grew better in higher fertility substrata. Species originating from periodically flooded ecosystems grew better than those from upland ecosystems. Nodulation was observed in only thirty species. Some non-nodulating species grew as fast as the nodulating ones, indicating that biological nitrogen fixation is not the only efficient mechanism of nitrogen acquisition for tropical legume species. Species with maximum growth rate were: Enterolobium maximum, Swartzia polyphylla and Vatairea guianensis.