Heavy metal accumulation in different growth forms of Spartina alterniflora.

摘要

Spartina alterniflora (smooth cordgrass) is a salt tolerant grass found along the east and southeast coasts of the United States. It is an ecologically important species in numerous marshes as it provides habitat and food and is often used in erosion control or phytoremediation. Three phenotypic growth forms of the species are recognized in Galveston Bay: short, intermediate, and tall. Numerous studies have measured the uptake, accumulation, and excretion of a variety of metals in S. alterniflora , but none appear to have compared these measures among growth forms. The objective of this study was to determine if different growth forms of S. alterniflora vary in: (1) the amount of heavy metals they uptake, or (2) in the locations in which heavy metals are accumulated within the plant. Grasses collected from Galveston Bay were exposed to one of five metal iv treatments (Cd, Cr, Cu, Pb, or Zn) hydroponically in the laboratory and then each tissue type was analyzed separately to measure heavy metal accumulation and excretion. No significant differences in metal concentrations were found among growth forms in the roots of exposed plants. However, leaves of the short form accumulated significantly more cadmium and lead, while stems and excreted salts of the short form contained significantly more lead and zinc. These results provide evidence of ecotypic variation in the accumulation of several metals, and indicate that taller forms of the species are more likely to restrict heavy metals to belowground biomass and decrease the bioavailability of contaminants.