Metallophytes possess a suite of adaptations that permit them to tolerate high levels of heavy metals in the soil environment. These plants and the unusual habitats that support them (eg. serpentine barrens, calaminarian grasslands) deserve high priority for conservation. This study is part of an ongoing effort to investigate the role of Ni in the growth, survivorship and reproduction of the Ni-hyperaccumulator, Alyssum murale. In view of the importance of maintaining the biodiversity of natural serpentine habitats, we are also interested in exploring potential ecological risks related to introducing Alyssum murale for phytoremediation of industrial soils and mine sites. This study used an additive design in a greenhouse study (16L;8D) to investigate the competitive ability of A. murale seedlings on soils with and without Ni. A high-drainage, low-nutrient soil mixture was made by combining coarse sand, fine gravel, and Fafard Mix #3 in a 1:1:2 ratio. The Ni soil treatment was amended with 500 mg/kg Ni in 1:1 ratio of Ni acetate and Ni sulfate.  Single focal A. murale plants were grown for 6 weeks in 5-cm plastic pots surrounded by a grass, Vulpia microstachys, commonly found in serpentine and non-serpentine habitats in the western US. The study included 37 replicates of 4 Vulpia density treatments: 0, 4, 8 and 12.  

Results/Conclusions

In both species, the rate of germination was not significantly affected by the presence of Ni. Two way ANOVA revealed significant effects of soil type (p=0.000) and Vulpia density (p=0.000) on Alyssum shoot height and biomass. Alyssum biomass was significantly greater in soils with Ni, and biomass decreased significantly as the density of Vulpia increased. A significant interaction between soil type and Vulpia density (p=0.000) was also found; the negative effects of Vulpia density on Alyssum biomass were stronger without Ni than with Ni. These results support our earlier studies that indicate Ni enhances growth in A. murale. Growth of A. murale seedlings significantly decreased in the presence of Vulpia, but this effect was less severe in soils containing Ni. This suggests that the competitive ability of Alyssum murale may be greater in serpentine habitats. This factor should be considered when evaluating the risks of introducing A. murale in areas with proximity to natural serpentine communities.  Long-term studies conducted under natural conditions are essential to understand the role of Ni in the life history of A. murale and to determine its competitive ability in serpentine and non-serpentine conditions.