Trace element transfer from two contaminated soil series to Medicago sativa and one of its herbivores, Spodoptera exigua

ABSTRACT

Alfalfa was cultivated in two potted soil series obtained from two sandy soils contaminated by Cu (SM) and metal(loids)/PAH (CD). Shoot production was monitored for 8 weeks. Then, larvae of Spodoptera exigua were reared on alfalfa of both soil series for eight days. A biotest (using Phaseolus vulgaris) was used to assess the soil phytotoxicity. Increasing soil contamination reduced P. vulgaris growth, but alfalfa growth was only reduced on the SM soil series. Exposure to the SM soil was mirrored by shoot Cu and Cr concentrations of alfalfa (respectively, in mg kg ⁻¹ DW, Cu and Cr ranged from 11.9 and 0.4 in the CTRL soil to 98.5 and 1.2 in the SM one). Exposure to the CD soil series was mirrored by shoot Zn concentrations (i.e., 48–91.6 mg kg⁻¹ DW). Internal metal(loid) concentrations of S. exigua remained generally steady across both soil series (respectively Cd 0.05–0.16, Cr 0.5–3.3, Cu 5.8–98.5, Ni 0.6–1.6, Pb 0.4–1.3, and Zn 57–337 mg kg⁻¹ DW), and most of the associated transfer factors were lower than 1. Here, due to the excluder phenotype of alfalfa across our TE contamination gradients, S. exigua could cope with high total metal(loid) concentration in both contaminated soils.

KEYWORDS:

• Biotransfer
• food web
• herbivore
• phytomanagement
• phytotoxicity

Acknowledgments

This work was supported by both the ANR CD2i (Phytochem) and the INTENSE project (ERA-net Facce surplus). Authors are members of INRA's ecotoxicologist network (http://www6.inra.fr/ecotox). Authors are grateful to M. Fabrice Vetillard, research technician at the UMR BIOGECO INRA 1202, Bordeaux, France, for his contribution to the design and the cage building. They also thank M. Eric Pesme and M. Damien Butin, from the Bordeaux Metropole for providing alfalfa seeds and access to the Chaban-Delmas site, as well as Lyonnet SA for work at the St-Médard d'Eyrans site.