Phytoremediation of urban soils contaminated with trace metals using Noccaea caerulescens: comparing non-metallicolous populations to the metallicolous ‘Ganges’ in field trials

Abstract

Urban soil contamination with trace metals is a major obstacle to the development of urban agriculture as crops grown in urban gardens are prone to accumulate trace metals up to toxic levels for human consumption. Phytoextraction is considered as a potentially cost-effective alternative to conventional methods such as excavation. Field trials of phytoextraction with Noccaea caerulescens were conducted on urban soils contaminated with Cd, Cu, Pb, and Zn (respectively around 2, 150-200, 400-500, and 400-700 μg g −1 of dry soil). Metallicolous (Ganges population) and non-metallicolous (NMET) populations were compared for biomass production and trace metal uptake. Moreover, we tested the effect of compost and fertilizer addition. Maximal biomass of 5 t ha −1 was obtained with NMET populations on some plots. Compared to Ganges-the high Cd-accumulating ecotype from South of France often used in phytoextraction trials-NMET populations have an advantage for biomass production and for Zn accumulation, with an average Zn uptake of 2.5 times higher. The addition of compost seems detrimental due to metal immobilization in the soil with little or no effect on plant growth.In addition to differences between populations, variations of growth and metal accumulation were mostly explained by soil Cd and Zn concentrations and texture. Our field trials confirm the potential of using N. caerulescens for both Cd and Zn remediation of moderately contaminated soils-with uptake values of up to 200 g Cd ha −1 and 47 kg Zn ha −1 -and show the interest of selecting the adequate population according to the targeted metal.

Root foraging and avoidance in hyperaccumulator and excluder plants: a rhizotron experiment

“…For example, nonmetalliferous accessions of N. caerulescens are often characterized by a lower biomass compared to accessions from metal-contaminated soils (Escarré et al 2013). Comparing a large number of N. caerulescens accessions, it was observed that calamine accessions produce the greatest shoot biomass (Sterckeman et al 2017), as also shown in our experiment. Haines (2002) reported that a higher plant biomass was obtained when roots of N. caerulescens were foraging for Zn; in our results, this effect was not observed for Ni, as no biomass variations were recorded in correspondence with higher Ni supply, Ni shoot uptake or root proliferation in Ni-enriched areas (Tables 1 and 2 ;Figs.…”

“…3 ), even if it was not statistically significant for the Plombieres accession growing in the garnierite treatment. Variability in growth rates between the two accessions of N. caerulescens can be related to the natural morphological and physiological differences in accessions of this species (Ingrouille and Smirnoff 1986;Sterckeman et al 2017). For example, nonmetalliferous accessions of N. caerulescens are often characterized by a lower biomass compared to accessions from metal-contaminated soils (Escarré et al 2013).…”

“…A peculiarity of this species is its occurrence on a variety of different substrates, ranging from uncontaminated "normal" soils to soils naturally enriched or contaminated soils with high concentrations of certain trace metals such as Ni, Zn and Cd. Even if occurring on uncontaminated soils, many populations of N. caerulescens can tolerate conditions on sites with anthropogenic metal pollution (Baker et al 1994;Ingrouille and Smirnoff 1986;Gonneau et al 2017;Meerts and Isacker 1997), including mine waste and smelter sites (Reeves et al 2001); while other populations occur on Ni-rich soils developed from ultramafic bedrocks in Europe (Meyer 2006;Reeves et al 2001;Sterckeman et al 2017).…”

“…Despite the contribution of recent studies to elucidate plant-internal processes associated with metal hyperaccumulation (Assunção et al 2003b;Brooks 1998;Krämer et al 1996Krämer et al , 1997Krämer et al , 2000Krämer 2010;Lombi et al 2000), increased knowledge about rhizosphere processes (Dessureault-Rompré et al 2010;Wenzel et al 1999Wenzel et al , 2003, the precise mechanisms by which hyperaccumulator plants take up metals from the soil is still relatively limited. Being a hyperaccumulator of different metals (Ni, Zn, Cd), N. caerulescens is receiving considerable scientific attention with the recognition of its usefulness in ecological, physiological and genetics and molecular biological studies of metal accumulation (Baker et al 1994;Craciun et al 2012;Halimaa et al 2014;Lasat et al 1996;Milner and Kochian 2008;Milner et al 2012;Puschenreiter et al 2003;Vàzquez et al 1992), and the key role of metalaccumulating plants in remediating metal-contaminated soils using phytotechnologies (Baker et al 1991;Brown et al 1994;Escarré et al 2000;Hammer and Keller 2003;Jacobs et al 2017Jacobs et al , 2018McGrath et al 1993McGrath et al , 2006Robinson et al 1998;Schwartz et al 2003).…”

Phytostabilization of Cd and Pb in Highly Polluted Farmland Soils Using Ramie and Amendments

“…In terms of different pollution levels, appropriate strategies should be used to maximize the phytoremediation effect. Phytoextraction, which uses hyperaccumulator plants to remove heavy metals from soil, is suggested for remediation of slightly and moderately contaminated soils [11,12], while phytostabilization is thought to be practical for remediation of multi-metal highly contaminated soils [13,14].…”