A phytogeochemical survey of the flora of ultramafic and adjacent normal soils in North Morocco

Variation in plant elemental composition (Ni, Ca, Mg, Mg/Ca ratio) in relation to soil composition was investigated in a poorly studied ultramafic area in the north of Morocco. A total of 142 leaf samples representing 36 species from 9 sites (5 ultramafic and 4 normal soils from adjacent areas) were analysed. The soil was richer in Mg and Ni and had a higher Mg/Ca ratio in the ultramafic sites than in the control sites, and these differences were qualitatively reflected in the average mineral composition of the plants. However, there were considerable differences in mineral composition among species within serpentinic sites, indicating that species with contrasting mineral nutrition strategies can cope with the mineral element imbalance characteristic of ultramafic soils. Particularly noteworthy was the finding that species with high requirements of Ca are not excluded from serpentinic soils. In view of their high responsiveness to soil nickel and magnesium concentration, Dittrichia viscosa and Lavandula dentata are proposed as bioindicators of these elements in the soil in the Rif area. By contrast, two local serpentine endemics, Halimium atriplicifolium and Notholaena marantae were excluders of nickel and magnesium.