Uptake and distribution of metals in two dominant salt marsh macrophytes, Spartina alterniflora (cordgrass) and Phragmites australis (common reed)

We examined patterns of biomass accumulation and tissue concentrations of five metals—mercury, copper, zinc, chromium, lead—and two elements—carbon and nitrogen—to determine differences in net metal accumulation and distribution between Phragmites australis (common reed) and Spartina alterniflora (cord grass) which were growing intermingled in a contaminated low marsh. Data were collected at two-month intervals across a growing season (April–October, 1999). Although they comprise only 5–15% of whole plant biomass for both species, roots consistently contained 70–100% of the whole plant metal burdens for both S. alterniflora and P. australis (shoot : root ratio < 0.42). Stems and rhizomes had low and similar concentrations between plant species throughout the summer. Leaves of S. alterniflora, however, had consistently greater concentrations of Hg and Cr than those of P. australis. In contrast, the micronutrients Cu and Zn were enriched in P. australis leaf tissue in October, compared to S. alterniflora. Pools of metal in aboveground biomass were similar between plant species, but throughout the season S. alterniflora allocated more of this burden to leaf tissue than P. australis, which allocated more of the aboveground burden to stem tissue, a recalcitrant tissue with lower concentrations but greater biomass. The consistently higher concentrations and total pools of Hg and Cr in S. alterniflora leaf tissue and higher Zn and Cu in P. australis may result from differences in leaf phenology, root-influenced metal availability, or transport of dissolved metals. Because S. alterniflora shifts more of its Hg and Cr load into highly decomposable leaf tissues (as opposed to recalcitrant stems, roots, and rhizomes) this pathway of metal bioavailability would be reduced when S. alterniflora is replaced by P. australis.