Paula Gonçalves* e Isabel Videira e Castro**²

* Aluna Estagiária

** Investigador Auxiliar

Estação Florestal Nacional. Departamento de Ecologia, Recursos Naturais e Ambiente. Quinta do Marquês, Nova Oeiras, 2784-505 OEIRAS

Sumário.A aplicação de lamas residuais urbanas na agricultura é uma prática que é utilizada mundialmente, com efeitos benéficos ao nível da produtividade das culturas, da matéria orgânica do solo, da sua capacidade de troca catiónica e de retenção da água. Porém, as lamas residuais podem ser portadoras de altas quantidades de metais pesados e de outros poluentes, que podem causar sérios problemas ambientais afectando quer as plantas (ao reduzir o peso das raízes, o número de folhas e a parte aérea) quer os microrganismos do solo, designadamente as bactérias Rhizobium (fixadoras de azoto). Com a finalidade de se avaliar as potencialidades de uma lama residual da área urbana de Lisboa, como fertilizante de uma pastagem mista de trevo subterrâneo e de azevém, foi instalado um ensaio de campo nos terrenos da Quinta do Marquês (Oeiras). No presente trabalho pretendeu-se examinar as possíveis alterações na diversidade genética da população natural de Rhizobium leguminosarum biovar trifolii, existente nestes solos aos quais se adicionaram diferentes quantidades de lamas residuais (5, 10, 20 e 50 t ha^-1). Os resultados obtidos permitiram-nos verificar que ocorreu uma mudança na composição genética, a nível de DNA-plasmídico nos isolamentos de Rhizobium testados, principalmente nos tratamentos onde foram adicionadas as quantidades mais elevadas de lamas (20 e 50 t ha^-1).

Palavras-chave: lamas residuais; Rhizobium; diversidade genética; perfis de plasmídeos

Abstract. The use of sewage sludge in agriculture is being practised throughout the world with beneficial effects on the productivity of cultures, on the organic content of soils, and on their capacity of cation exchange and water retention. However, sewage sludge can contain high concentrations of heavy metals and other contaminants that may cause serious environmental problems, affecting both plants and soil microorganisms, especially Rhizobium bacteria (nitrogen fixers). To evaluate the potentialities of an urban sewage sludge from Lisbon as a fertiliser for underground clover and grass pastures, a field experiment was carried out in the grounds of Quinta do Marquês (Oeiras). The aim of this work was to monitor changes in the genetic diversity of Rhizobium leguminosarum biovar trifolii population in soils amended with different quantities of sewage sludge (5, 10, 20 and 50 t ha^-1). The results of this study permitted us to verify that changes took place at the plasmid-DNA level in the genetic composition of the Rhizobium isolates tested, primarily where treatments had been amended with high quantities of sewage sludge (20 and 50 t ha^-1).

Key-words: sewage sludge; Rhizobium; genetic diversity; plasmid profile

Effects de la Application de Boues d'Épuration Dans la Diversité de la Population Rizobienne du Sol

Résumé. L'application de boues d'épuration urbaines dans l'agriculture est un procédé utilisé mondialement. Ce procédé apporte des bénéfices au niveau de la productivité, des matières organiques, de la capacité d'échange cationique et de la rétention d'eau. Toutefois, les boues d'épuration peuvent apporter de grandes quantités de métaux lourds et d'autres polluants qui peuvent originer de sérieux problèmes ambientaux qui affectent les plantes, ainsi que les microorganismes du sol, comme les bactéries Rhizobium (fixatrices d'azote). Pour évaluer les potentialités d'une boue d'épuration urbaine de Lisbonne comme fertilisant pour un pâturage de trèfle souterrain et grasse, une recherche a été effectuée sur le sol de la "Quinta do Marquês" (Oeiras). Cette recherche a permis d'examiner les modifications dans la diversité génétique de la population naturelle du Rhizobium leguminosarum biovar trifolii existant dans le sol additionné de différentes quantités de boues d'épuration (5, 10, 20 et 50 t ha^-1). Les résultats obtenus ont permis de remarquer un changement dans la composition génétique, au niveau du DNA-plasmidique des isolements de Rhizobium testés, surtout dans les traitements où de plus grandes quantités de boues (20 et 50 t ha^-1) avaient été ajoutées.

Mots clés: boues d'épuration; Rhizobium; diversité génétique; profils de plasmides

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