High soil nickel enhances seed weight and seedling growth in Alyssum murale, a nickel-hyperaccumulator

Background/Question/Methods

Alyssum murale Waldst and Kit.(Brassicaceae) is a nickel-hyperaccumulator plant originating in serpentine areas in the Mediterranean.  Although this species grows on serpentine and non serpentine soils, little is known about its ecological response to soil nickel.  Understanding this response is important because the role of edaphic factors in influencing endemism and competitive ability of serpentine species has long been of interest to plant ecologists. In addition, because Alyssum murale is under development for phytoremediation and phytomining of nickeliferous soils in North America, it is important to explore the potential for this species to spread inadvertently to non-nickeliferous soils adjacent to target sites. This study examined the effect of seed origin, soil type, and seed weight on the growth and survivorship of A. murale seedlings. Seeds from plants grown with or without nickel were individually weighed and planted singly in 2 in² plastic cells containing pure Sunshine mix or Sunshine mix amended with 500 ppm nickel (1:1 Ni acetate: Ni sulfate). Effects of seed origin and soil type were compared by two-way ANOVA with seed weight as a covariate.

Results/Conclusions

Seeds produced by plants grown in soil with nickel had significantly greater seed weight (p=0.020), germination percentage (p=0.000) and shoot weight (p=0.009). Seed weight had a significantly positive effect on germination (p=0.000), leaf number (p=0.026), shoot weight (p=0.042) and root weight (p=0.008) after six weeks.  Although A. murale germinated equally well on soil with and without nickel, seedlings grown in soil with nickel had significantly greater numbers of leaves (p =0.000), shoot biomass (p=0.000) and root biomass (p=0.000) after six weeks. The strong positive growth response in the presence of nickel combined with the seed weight advantage of offspring originating on nickel soils, suggests nickel plays a powerful role in influencing seedling fitness in A. murale.  This positive response to soil nickel may influence the colonization patterns and competitive ability of Alyssum murale on serpentine and non-serpentine soils. Further studies are underway to examine the competitive ability of Alyssum murale on nickeliferous and non-nickeliferous soils.