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Avaliou-se a actividade das enzimas antioxidativas (catalase, peroxidase e superóxido dismutase) e as concentrações em As, Cu, Pb e Zn nas folhas de duas populações de Cistus ladanifer L. colhidas, na Primavera e no Verão, em solos não contaminados em elementos vestigiais (Caldeirão e Pomarão) e com condições climáticas diferentes. Nos solos das duas áreas, as concentrações totais e disponíveis (extracção com DTPA) em elementos vestigiais foram baixas. A distribuição dos elementos pelas folhas novas e maduras foi semelhante entre áreas e estações do ano. As actividades enzimáticas variaram consoante a população. As folhas colhidas nas duas estações do ano, excepto as folhas novas de Verão do Pomarão, apresentaram actividade enzimática na fracção solúvel e iónica. Comparando as estações do ano e áreas de amostragem, constatou-se que as actividades enzimáticas representam um mecanismo de tolerância a vários factores de stresse (radiação UV, temperatura do ar elevada no verão, défice hídrico no verão, baixa-média fertilidade do solo e conteúdo de elementos vestigiais no solo), o que confere uma elevada plasticidade à espécie.The aim of this study was to evaluate the antioxidant enzymes activity (catalase, peroxidase and superoxide dismutase) and the concentrations of As, Cu, Pb and Zn in leaves from two populations of Cistus ladanifer growing on soils non-contaminated with trace elements (Caldeirco and Pomarco), but with different climatic conditions and in two different seasons (spring and summer). In both areas, total and available concentrations (DTPA extraction) of trace elements in soils were low. The distribution of elements for young and mature leaves was similar between areas and seasons. The enzyme activities varied with the plant population. Leaves collected in the two seasons, except young leaves from Pomarco collected in summer, showed enzymatic activity in the soluble and ionic fractions. Comparing the seasons and sampling areas, C. ladanifer enzymatic activities represent a tolerance mechanism to different stress factors (UV radiation, high air temperature in summer, drought, low-medium fertility in soils, trace element concentrations in soil), giving it a high plasticity.

The procedure of BCR sequential extraction has been applied to five samples from two unpolluted soils in southern Spain. Total concentrations of different elements have been calculated as the sum of the three fractions of BCR and the residue has been measured for each. Also, a total analysis based on INAA or total-digestion techniques has been performed for the same samples. BCR and total analysis closely agreed for As, Pb and Cd. For Cu, Co, Cr and Zn the comparison of the results did not provide definitive conclusions concerning the capability of BCR in measuring total concentrations. On the other hand, in these cases, a certain correlation was found between the concentrations measured and some soil characteristics, especially the clay, organic-matter and CaCO3 contents. BCR proved incapable of providing accurate measurements for Ni. [Copyright &y& Elsevier]