Differential elemental uptake in three pseudo-metallophyte C4 grasses in situ in the eastern USA

Abstract

Background and aims: Elemental uptake in serpentine floras in eastern North America is largely unknown. The objective of this study was to determine major and trace element concentrations in soil and leaves of three native pseudo-metallophyte C₄ grasses in situ at five sites with three very different soil types, including three serpentine sites, in eastern USA.

Methods: Pseudo-total and extractible concentrations of 15 elements were measured and correlated from the soils and leaves of three species at the five sites.

Results: Element concentrations in soils of pseudo-metallophytes varied up to five orders of magnitude. Soils from metalliferous sites exhibited higher concentrations of their characteristic elements than non-metalliferous. In metallicolous populations, elemental concentrations depended on the element. Concentrations of major elements (Ca, Mg, K) in leaves were lower than typical toxicity thresholds, whereas concentrations of Zn were higher.

Conclusions: In grasses, species can maintain relatively low metal concentrations in their leaves even when soil concentrations are richer. However, in highly Zn-contaminated soil, we found evidence of a threshold concentration above which Zn uptake increases drastically. Finally, absence of main characteristics of serpentine soil at one site indicated the importance of soil survey and restoration to maintain serpentinophytes communities and avoid soil encroachment.

Keywords: C4 grass; Calamine; Pseudo-metallophytes; Serpentine; accumulation; excluder.

Fig. 1

CAP ordination space of elemental concentrations in a pseudo-total, b extractible and c in leaves with position of species in blue and site in red. NOT: Nottingham, SGW: Sugartown, UNI: Unionville, PAL: Palmerton and FIG: Fort Indiantown Gap

Fig. 2

Concentrations of Ca and Mg (mg kg⁻¹) in five sites in ENA: pseudo-total, extractible and in leaves. NOT: Nottingham, SGW: Sugartown, UNI: Unionville, PAL: Palmerton and FIG: Fort Indiantown Gap

Fig. 3

Concentrations of Ni and Zn (mg kg-1) in five sites in ENA: pseudo-total, extractible and in leaves. NOT: Nottingham, SGW: Sugartown, UNI: Unionville, PAL: Palmerton and FIG: Fort Indiantown Gap

Fig. 4

Correlation between major and trace elements concentrations in leaves at a Nottingham, Unionville and S. scoparium at Sugartown, b soil from A. gerardii and S. nutans at Sugartown, c Palmerton and d Fort Indiantown Gap. The three species at Sugartown were separated into two groups after our soil analyses indicated that S. scoparium clustered with the serpentine group while A. gerardii and S. nutans did not