To identify Cd- and Zn-accumulating plants exhibiting a high growth rate, seeds from the halophyte species Mediterranean saltbush (Atriplex halimus L.) were collected on a heavy-metal-contaminated site in southeastern Spain (Llano del Beal, Cartagena). Seedlings from this ecotype were exposed for 3 wk to 0.1 mM Cd or Zn in a nutrient solution in a fully controlled environment. All plants remained alive and no significant growth inhibition was recorded until the end of the experiment. Mean Cd and Zn accumulation in aerial parts was 830 and 440 mg kg(-1), respectively, and the rate of metal translocation even increased with the duration of stress exposure. Resistance to heavy metals in this species may be partly linked to precipitation of Cd in oxalate crystals in the stems. A Cd-induced decrease in glutathione concentration also suggests that phytochelatins overproduction may occur in these conditions. We conclude that Mediterranean saltbush, which is able to produce up to 5 Mg dry matter ha(-1) yr(-1), may be an effective species for phytoextraction and should be tested for this purpose in field conditions.
Summary• We examined phenotypic plasticity of fitness components in response to zinc (Zn) in the Zn hyperaccumulator, Thlaspi caerulescens .• Two populations from Zn-enriched soils (M) and two populations from normal soils (NM) were grown in pots at three Zn concentrations (0, 1000 and 8000 mg kg − 1 Zn), for an entire life cycle. Growth, Zn accumulation and fitness components were assessed.• Based on vegetative growth, M and NM populations had similar Zn tolerance at 1000 mg kg − 1 Zn. However, reproductive output was markedly decreased in NM at 1000 and 8000 mg kg − 1 Zn. In M populations, Zn did not affect fitness. However, low Zn status enhanced reproductive output in year 1 compared with year 2 and decreased survival after the first flowering season.• M populations are able to achieve equal fitness across a broad range of Zn concentrations in soil by different combinations of fecundity and longevity. No cost of higher tolerance was demonstrated in M populations. Reproductive traits appeared to be a more sensitive indicator of tolerance than vegetative growth.
Summary• 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 ). 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.
Summary• Field reciprocal transplantations of two metallicolous populations (Mpops) and two nonmetallicolous populations (NMpops) of Thlaspi caerulescens were performed here to determine the pattern of local adaptation and to assess the cost of adaptation of Mpops to a metalliferous environment (Menv). The role of herbivores as an important selective pressure in the nonmetalliferous environment (NMenv) was also examined.• Growth, survival, fitness, life cycle and herbivore consumption were monitored for each transplant for 2 yr.• Local adaptation of Mpops to their own environment was clearly demonstrated, as Mpops consistently outperformed NMpops in Menv. In NMenv, no advantage of NMpops over Mpops was detected. However, the fitness of Mpops was generally lower in NMenv than in Menv. Herbivore consumption appeared to be a significant selective pressure for Mpops in NMenv.• An imbalance of selective forces between Menv and NMenv probably explains the greater local adaptation of Mpops. Therefore, colonization of NMenv by Mpops appears possible. Although Mpops were able to survive and reproduce in NMenv, they nevertheless expressed a cost attributable in part to their higher susceptibility to herbivores.
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