Thlaspi caerulescens on nonmetalliferous soil in Luxembourg: ecological niche and genetic variation in mineral element composition

Forty-seven populations of Thlaspi caerulescens in Luxembourg were characterised for population size, soil mineral element composition and other habitat characteristics. Foliar concentrations of eight elements were assessed in 15 populations in the field and in eight populations cultivated in zinc (Zn)-cadmium (Cd)-nickel (Ni)-enriched soil. T. caerulescens favoured stony soil developed on steep, south-facing Emsian shale outcrops. All soil samples were nonmetalliferous. Soil pH ranged from 4.2 to 6.9. Field-growing plants had very high concentrations of heavy metals in the leaves (Zn, 3000-13 000 mg kg(-1); Cd, 11-44 mg kg(-1); Ni, 38-473 mg kg(-1)). Positive soil-plant correlations existed for Zn and Mn. In cultivation, significant genetic variation was found for biomass and six of eight mineral elements. For Cd and Zn, variation range among 48 half-sib families was two-fold (Cd, 183-334 mg kg(-1); Zn, 8030-16 295 mg kg(-1)). Most of the variation occurred among populations, consistent with the selfing mating system of those populations. There was a tight Zn-Cd genetic correlation (r = +0.83, P < 0.0001). The significance of the results to the conservation of T. caerulescens in Luxembourg is briefly discussed.