Overview
This invited narrative review for the Castanea themed treatment of southeastern serpentine ecology synthesizes the published and previously unpublished evidence on heavy-metal-tolerant and hyperaccumulating plants in the southeastern United States, framed around the two best-studied serpentine outcrops (Soldiers Delight, MD; Buck Creek, NC) and the cobalt and manganese hyperaccumulators Nyssa spp. and Phytolacca americana. Previously unpublished foliar nickel data from five woody species at Buck Creek (mean across all sample points 15.3 µg g⁻¹ dry leaf, N=146) confirm that woody plants on this serpentine barren take up Ni at the upper end of the typical serpentine range (5–100 µg g⁻¹) but far below the 1,000 µg g⁻¹ hyperaccumulation threshold. The review reports no food, beverage, ingredient, or supply-chain measurements and is plant-ecology evidence rather than direct food-system evidence; relevance to the wiki is as upstream context for soil-to-plant uptake of Ni, Mn, and Co in temperate-USA conditions, and for the geochemical baseline of ultramafic soils.
Key numbers
Previously unpublished foliar Ni at Buck Creek, NC (PDF p. 261, Figure 1)
Mean foliar Ni (µg g⁻¹ dry leaf) by species and sampling date, leaves collected June, July, and October 2005 at 10 transect points (the source does not report per-species or per-date N; only the pooled total N=146 is given):
- Acer rubrum (AR): June ~5.5, July ~5.5, October ~4 µg g⁻¹.
- Magnolia acuminata (MA): June ~28.5, July ~27.5, October ~19 µg g⁻¹.
- Quercus alba (QA): June ~11.5, July ~15.5, October ~16.5 µg g⁻¹.
- Sassafras albidum (SA): June ~37.5, July ~22, October ~30 µg g⁻¹.
- Tsuga canadensis (TC): June ~6, July ~6, October ~4 µg g⁻¹.
(Bar-chart readout from Figure 1; the source does not provide an underlying numeric table for these means.)
- Pooled foliar Ni across species, sites, and dates: mean 15.3 µg g⁻¹, N=146, SEM=0.85 (PDF p. 262).
- Litter-fall Ni return estimate: >30 g Ni ha⁻¹ y⁻¹ (multiplying mean foliar Ni by published canopy-biomass estimate from Johnson and Henderson 1989; PDF p. 262).
- Pre-existing serpentine-vegetation benchmark: Reeves et al. 1996 (cited) state most serpentine plants carry foliar Ni 5–100 µg g⁻¹ (≈10× nonserpentine soils); the Buck Creek mean sits in this range. Acer rubrum and Tsuga canadensis values track the lower bound, consistent with low accumulation reported by Andersen et al. 1999.
Buck Creek serpentine soil Ni (PDF p. 263, Figure 2; eight sampling dates June 2005–May 2006, two horizons, two extractions)
Soil Ni (µg g⁻¹ dry soil), log-scale readout from Figure 2:
- A-horizon (mineral topsoil), strong-acid digestion (total Ni): approximately 800–1,500 µg g⁻¹ across all eight dates.
- O-horizon (organic), strong-acid digestion: approximately 350–500 µg g⁻¹ across all eight dates.
- A-horizon, ammonium-acetate extraction (exchangeable / bioavailable Ni): approximately 3–10 µg g⁻¹ across all dates.
- O-horizon, ammonium-acetate extraction: approximately 2–8 µg g⁻¹; a single February 2006 spike reached ~10 µg g⁻¹, attributed to soil thaw and rapid litter decomposition.
ANOVA on strong-acid Ni (total Ni in soil matrix): horizon effect F(1,102) = 132.60, p<0.0001; sampling-date effect F(7,102) = 1.69, p = 0.1186 (not significant). ANOVA on ammonium-acetate Ni (exchangeable): horizon effect F(1,124) = 28.31, p<0.0001; sampling-date effect F(7,124) = 2.19, p = 0.0390; horizon-by-date interaction F(7,124) = 2.35, p = 0.0273 (PDF p. 262).
Phytolacca americana, Mn-mine sites near Cherokee County, SC (PDF p. 265, 2010 survey)
- Soil Mn: mean 7,765 µg g⁻¹, N=6, SEM=2,398, maximum 17,556 µg g⁻¹ (~1.8 percent Mn by mass).
- Leaf Mn in P. americana: mean 4,388 µg g⁻¹ dry leaf, N=14, SEM=707, maximum 10,089 µg g⁻¹ (just exceeds the 10,000 µg g⁻¹ Mn hyperaccumulation threshold).
- Comparative published Chinese mine-tailings soil Mn: 81,580 µg g⁻¹ mean (Xue et al. 2004), an order of magnitude higher than the SC sites.
Hyperaccumulation thresholds adopted by the review (PDF p. 263, citing van der Ent et al. 2013)
Concentrations defining hyperaccumulation (µg metal g⁻¹ dry leaf tissue): Cd, Se, Tl 100; Co, Cr, Cu 300; As, Ni, Pb 1,000; Zn 3,000; Mn 10,000. Approximately 580 vascular-plant taxa worldwide qualify, less than 0.2 percent of vascular plants; more than 450 of these are Ni hyperaccumulators on serpentine.
Cobalt hyperaccumulation in southeastern Nyssa (PDF p. 264, narrative)
Most Nyssa studies report foliar Co 50–100 µg g⁻¹; N. sylvatica may surpass the 300 µg g⁻¹ Co-hyperaccumulation threshold, and cultivation trials of N. aquatica and N. biflora with exogenous Co can also exceed the threshold (McLeod and Ciravolo 2007 cited). No primary measurements reported in this paper for Co.
Methods (brief)
Buck Creek leaf samples: rinsed, oven-dried, weighed, ashed 12 h in a muffle furnace at 500 °C, ashes dissolved in 1 mL of 10 percent nitric acid and diluted with 4 mL deionized water, filtered to remove undissolved particles, analyzed by flame atomic absorption spectrophotometry on an Instrumentation Laboratory model IL551 (Wilmington, MA). Preliminary scans indicated Cr and Co in leaf samples were near or below detection limits; subsequent measurements focused on Ni. Soil samples: homogenized, sieved 2 mm; strong-acid digestion on 1 g dry soil boiled 6 h in 1.5 mL of 12.1 M HCl plus 0.5 mL of 15.6 M HNO₃, filtered and brought to 25 mL; ammonium-acetate extraction on 2.5 g dry soil with 33 mL of 0.5 M ammonium acetate in three sequential 30 min extractions on an orbital shaker, centrifuged at 5,000 ×g, combined supernatants brought to 100 mL. Phytolacca survey (2010): leaf digestion procedure identical to Buck Creek except smaller samples were used and ash dissolved in HCl. Statistical analysis by two-way ANOVA on horizon and sampling date. No LOD or LOQ values are reported for either analyte in the published text. Evidence tier B: the page is a peer-reviewed narrative review framing previously unpublished primary measurements within a literature synthesis; the primary data are limited in scope (single serpentine outcrop, single tree-species set, single sampling year) and the review carries no PRISMA flow or systematic risk-of-bias assessment.
Implications
Certification: Plant-ecology evidence with no direct food-system measurements. The Buck Creek foliar-Ni distribution (woody species 4–37 µg g⁻¹ dry leaf, weighted mean 15.3 µg g⁻¹) sits below the lower end of foliar Ni concentrations relevant to leafy-vegetable food crops grown on metalliferous soils and is therefore not a direct contribution to HMTc Ni threshold work. The paper does, however, establish a temperate-USA serpentine soil-Ni baseline (A-horizon total ~1,000 µg g⁻¹, exchangeable ~3–10 µg g⁻¹) useful as context for any future ingestion of food-crop work on US ultramafic-influenced soils.
Courses: Strong illustrative case for educator content on plant uptake of heavy metals from soil — the order-of-magnitude gap between total soil Ni (~1,000 µg g⁻¹) and exchangeable Ni (~5 µg g⁻¹) is a clean teachable example of why total-soil concentrations alone are poor predictors of plant uptake. The cobalt hyperaccumulation discussion in Nyssa is a useful counterexample to the popular framing that hyperaccumulation is exclusively a Ni-on-serpentine phenomenon.
App: Not directly applicable to any ingredient contamination_profile block; no consumer-facing food matrices measured. No app-layer changes triggered by this source.
Microbiome: Not addressed.
Provenance notes
Open-access via BioOne’s full-text URL (bioone.org/doi/full/10.2179/16-084); the BioOne Terms of Use permit personal, educational, and non-commercial use only. Citation: Pollard, A. J. 2016. Castanea 81(4): 257–269. Department of Biology, Furman University, Greenville, SC. DOI 10.2179/16-084. Received January 11, 2016; accepted August 29, 2016.
Related evidence
Update history
No substantive edit history is available in this build. The full commit record is available in git.