Phytoextraction of cobalt (Co)-contaminated soils by sweet alyssum (Lobularia maritima (L.) Desv.) is enhanced by biodegradable chelating agents

Purpose: Combining biodegradable chelating agents with phytoextraction is an efficient technique to amend metal-contaminated soils, but most studies have addressed remediation efficiency rather than a comprehensive understanding of the interactions among plant stress, metal accumulation, and metal bioavailability. This study aimed to investigate the effects of biodegradable chelating agents on improving the efficiency of phytoextraction for cobalt (Co)-contaminated soil by sweet alyssum (Lobularia maritima (L.)) and to explore the interrelationships among plant stress, Co accumulation, and Co bioavailability. Materials and methods: Sweet alyssum (three plants per pot) was grown in pots containing soil with Co added at 0, 40, and 60 mg kg−1, respectively. After 70 days of growth, we added four biodegradable chelating agents (EDDS, NTA, CA, and OA) at various concentrations (0, 2.5, 5.0, and 7.5 mmol kg−1). The plants were harvested after 7 days, and the biomass, reactive oxygen species (ROS) parameters, Co concentrations of the shoot and root, and available Co content in the soil were analyzed. Results and discussion: The results demonstrate that chelating agents significantly (p < 0.05) improved the phytoextraction capability of sweet alyssum and influenced plant growth and stress. The capability of EDDS to activate Co was higher than that of other chelating agents at identical concentrations in Co-contaminated soils. Furthermore, we observed that a moderate concentration (40 mg kg−1) of Co could promote plant growth and that high concentrations of Co (60 mg kg−1) and EDDS (7.5 mmol kg−1) cause enhanced stress to plant growth, even resulting in lower shoot Co accumulation than that in the moderate EDDS treatment (5.0 mmol kg−1). Conclusions: The present study demonstrates that the application of EDDS may be a better choice for Co phytoextraction than NTA, CA, and OA; nevertheless, a high concentration of EDDS may enhance the negative effects on plant growth, physiological traits, and Co accumulation.