Offspring of metal contaminated saltmarsh (Juncus acutus) exhibit tolerance to the essential metal Zn but not the nonessential metal Pb

Halophytes residing in metal-contaminated saltmarsh habitats may employ strategies to enhance fitness of the next generation. We aimed to test the hypothesis that Juncus acutus individuals inhabiting metal-contaminated locations would experience elevated tolerance of offspring to metals compared to plants residing in locations with no metal contamination history. J. acutus seeds (F1 generation) were collected from F0 parent plants residing at eight locations of a contemporary sediment metal gradient (contaminated to uncontaminated) across the coast of NSW, Australia (Hunter river, Lake Macquarie and Georges River). Seeds were exposed in the laboratory to incremental Zn (0.0–1.6 mM) and Pb (0.0–0.50 mM) for nine (9) days, and % germination, germination rate, root elongation and vigour index were assessed for the determination of tolerance. Greater root accumulation (BCF = 1.01) of Zn and subsequent translocation to aerial parts (culm BCF = 0.58 and capsule BCF = 0.85) were exhibited in parents plants, whereas Pb was excluded from roots (BCF = 0.60) and very little translocation to aerial portions of the plant was observed (culm BCF = 0.02 and capsule BCF = 0.05). F1 offspring exhibited tolerance to Zn with EC50 (% germination) significantly correlated with their parents' culm (R2 = 0.93, p = 0.00) and capsule (R2 = 0.57; p = 0.03) Zn. No correlations were observed between offspring Pb tolerance and Pb in parents’ plant tissues. Enhanced tolerance to the essential metal Zn may be because Zn is very mobile in the parent plant and seeds experience greater Zn load as a significant portion of sediment Zn reaches capsules (85%). Thus, Zn tolerance in J. acutus seeds is likely attributable to acclimation via maternal transfer of Zn; however, further manipulative experiments are required to disentangle potential acclimation, adaptation or epigenetic effects in explaining the tolerance observed.