Interactions between the Hyperaccumulator Noccaea caerulescens and Brassica juncea or Lupinus albus for Phytoextraction

Abstract

Trace-element-contaminated soils cause environmental concern and represent a source of contamination for surrounding areas. Phytoremediation uses plants to diminish the environmental risks associated with this contamination. When the final aim is the extraction of the pollutants, this technique requires the use of plants that are able to accumulate high concentrations of the target elements in their aerial part, while producing high plant biomass. Here, pot experiments were carried out in order to determine the interaction between a hyperaccumulator (Nocaea caerulescens) and a metal excluder (Lupinus albus) or an accumulator (Brassica juncea) species regarding their trace element accumulation/exclusion capacity when sharing the rhizosphere. The plants were grown alone or were cocultivated in soils with different levels of trace element contamination. The Zn concentration in N. caerulescens plants was lower in cocultivation with B. juncea than when they were grown alone, indicating competition between the two species for Zn uptake. Contrastingly, when grown with L. albus, the Zn concentrations in N. caerulescens plants were higher than when grown alone. Therefore, under climatic conditions adequate for N. caerulescens growth, cocultivation with L. albus could favor Zn phytoextraction, while in the case of B. juncea, crop rotation rather than cocultivation is recommended for efficient phytoextraction.

Brassica Species in Phytoextractions: Real Potentials and Challenges

“…However, intercropping with Brassica species may lead to opposite effects, i.e., reduction in the uptake of the target element. The study conducted by Martínez-Alcalá et al [133] showed that Zn uptake in B. juncea and Noccaea caerulescens was significantly higher in monoculture compared to intercropping. The reason for this result is the competition between these two species in Zn uptake as well as their incompatibility in pH values optimal for growth, so crop rotation instead of intercropping could be beneficial for Zn extraction.…”

“…However, in pot experiments, the number of plants is often higher than is optimal, which affects plant growth and biomass yields. In several studies, a small amount of soil, equal or less than 0.5 kg, was used [103,113,115,124,125,133] for growing three [103] or ten plants [124]. Other studies reported higher quantities of polluted soil used for pot experiments.…”

“…In several experiments, seeds of Brassica species were not sown directly in the contaminated soil. Plants were first germinated for a week or two in sterilized and humidified vermiculite [115], sand [133], or unpolluted substrate [116,162] and then transferred to pots with contaminated soil. Germination of the plants in ab unpolluted environment helps their development in the early, most sensitive phase of growth and ensures that strong and healthy plants are used for the experiments.…”