Responses and resistance capacity of Solanum nigrum L. mediated by three ecological category earthworms in metal-[Cd-As-Cu-Pb]-contaminated soils of North China.

Earthworms play vital functions affecting plant growth and metal accumulation from downground to aboveground. Soil metal mobilization may be combined with use of earthworm and hyperaccumulator-Solanum nigrum to improve its remediation efficiency. Understanding the effects of specific-species earthworm belonging to different ecological categories on mechanisms underlying of S. nigrum is critical for metal-polluted remediation. However, seldom studies concerned earthworm-assisted phytoremediation of metal contaminated soil in Northern China. This study investigated the effects of earthworm (Eisenia fetida, Amynthas hupeiensis and Drawida gisti) on S. nigrum with exposure to uncontaminated and [Cd-As-Cu-Pb]-contaminated soil (referred to as S0 and S1) for 60 days, respectively. In S1 soil, A. hupeiensis (anecic) had stronger effects on growth and metal accumulation in the organs (root, stem, and leaf) of S. nigrum than D. gisti (endogeic) and E. fetida (epigeic), attributing to their ecological category. The BAF values of S. nigrum were generally ranking in Cd (0.66-5.13) > As (0.03-1.85) > Cu (0.03-0.06) > Pb (0.01-0.05); the BAFCd values were ranking in leaf (2.34-5.13) > root (1.96-4.14) > stem (0.66-1.33); BAFAs, BAFCu, and BAFPb were root (0.04-1.63) > stem (0.01-0.09) ≈ leaf (0.01-0.06). A. hupeiensis decreased the TF values of S. nigrum from the roots to the shoots. Co-effects of metal stress and earthworm activity on metal uptake by shoots suggested that A. hupeiensis increased the uptake of As, Cu, and Pb (by 56.3 %, 51.5 %, and 16.2 %, p < 0.05), but not Cd, which appeared to remain steady for prolonged durations. Alterations in the integrated biomarker response index version 2 (IBRv2) values demonstrated that A. hupeiensis (12.65) improved the resistance capacity (stimulated GSH, SnGS1, and SnCu-SOD) of S. nigrum under metal-containing conditions, compared with E. fetida and D. gisti (IBRv2 were 9.61 and 9.11). This study may provide insights into the patterns of 'soil-earthworm-plant system' on improving remediation efficiency of S. nigrum, from the perspective of earthworm ecological niche partitioning.

Responses and detoxification mechanisms of earthworm Amynthas hupeiensis to metal contaminated soils of North China.

Metal contamination is widespread, but only a few studies have evaluated the toxicological risks of metals (Cd, Cu, and Pb) in earthworms from farmlands in North China (Hebei province). Amynthas hupeiensis, the dominant species in the study area, was used to determine the responses and detoxification mechanisms of uncontaminated (CK), and low (LM)-, and high (HM)-metal-contaminated soils following 7-, 14-, and 28-days exposure. Metal toxicity in LM and HM soils inhibited the biomass of A. hupeiensis. The concentrations of Cd in A. hupeiensis bodies indicated accumulated Cd appeared to remain steady with prolonged exposure, while Cu/Pb increased significantly with soil levels. Bioaccumulation occurred in the order Cd > Pb > Cu in LM soil, and in the order Cd > Cu ≈ Pb in HM soil, which was attributed to differences in available fractions between LM and HM soils. Physiological levels of biomarkers in A. hupeiensis were determined, including total protein (TP), glutathione (GSH), glutathione peroxidase (GPx), acetylcholinesterase (AChE), and malondialdehyde (MDA). Deviations in GSH, GPx, and AChE were considered to denote sensitive biomarkers using the IBRv2 index. Metabolomics data (1H nuclear magnetic resonance-based) revealed changes in metabolites following 28-days exposure to LM and HM soils. Differences in metabolism in A. hupeiensis following exposure to LM and HM were related to energy metabolism, amino acid biosynthesis, glycerophospholipid metabolism, inositol phosphate metabolism, and glutathione metabolism. Metal stress from LM and HM soils disturbed osmoregulation, resulting in oxidative stress, destruction of cell membranes and inflammation, and altered levels of amino acids required for energy by A. hupeiensis. These findings provide biochemical insights into the physiological and metabolic mechanisms underlying the ability of A. hupeiensis to resist metal stress, and for assessing the environmental risks of metal-contaminated soils in farmland in North China.