Alyssum murale (Brassicaceae) originates from the Mediterranean region and is primarily found on serpentine soils. Serpentine soils have low fertility, high Mg and high levels (2000-5000 ppm) of Ni, a toxic metal. A. murale hyperaccumulates 2% Ni into its shoots. Alyssum montanum (Brassicaceae) is also native to the Mediterranean but it is a non-accumulator. Both species are herbaceous perennials adapted to arid, infertile soils. They produce many small, yellow flowers resulting in abundant small seeds. Our research focused on exploring whether non-accumulators and hyperaccumulators respond differently to the presence of nickel in the soil.

We examined the effect of soil nickel on germination and growth of A. montanum and A. murale.  Seeds were planted singly in 50-cell trays containing commercial soil with or without added nickel (1:1 Ni sulfate:Ni acetate). For A. murale, 2 Ni levels were used: 0 and 500 ppm.  For A. montanum, 5 Ni levels were used: 0, 10, 50, 200 and 500 ppm.  Germination and growth were monitored in a greenhouse for 6 weeks. Plants were harvested and dried at 70°C for 3 days, and biomass of individual seedlings was obtained.  

Results/Conclusions

Soil Ni inhibited germination in the non-accumulator, and no seedlings emerged in soil Ni levels greater than 50 ppm.  Soil Ni had no effect on germination in the hyper-accumulator, and high levels of Ni enhanced seedling growth. Emergence of A. montanum seedlings is significantly inhibited by soil Ni levels greater than 10 ppm (p=0.000). Seedling height and shoot weight in A. montanum are not significantly different in soil Ni levels from 0-50 ppm. In contrast, A. murale shows similar emergence in soils with 0 or 500 ppm Ni added. But seedling height and shoot weight of A. murale are significantly greater at 500 ppm Ni compared to 0 ppm (height: p=0.013; weight: p=0.000).

These differences are likely to result in different patterns of colonization by the two species under natural conditions. It is unlikely that Alyssum montanum will survive in serpentine habitats, since germination is strongly inhibited by low levels of soil nickel. Alyssum murale is likely to colonize serpentine and non-serpentine soils, since it germinates equally well on the two substrates. The presence of nickel in the soil may increase the competitiveness of A.murale in serpentine habitats since seedling growth is enhanced by nickel.  Further studies are underway to examine the mechanisms by which nickel enhances growth of Ni-hyperaccumulators.