Biomass and Nickel Tolerance: Canavalia ensiformis (L.) DC. as a Candidate Plant for Phytoremediation Applications

The use of high biomass production plants in studies of metal phytoremediation is an established practice. This strategy aims to identify plants that tolerate unusual amounts of metals such as nickel (Ni). When comparing the biomass production capacity of a Ni hyperaccumulator, such as plants from the Alyssum genus, a production ranging from 0.5 to 4 t ha−1 per crop cycle is observed ; on the other hand, species with a high biomass production capacity, for example Canavalia ensiformis, can produce 20 t ha−1 to 25 t ha−1 of green phytomass, 5 t ha−1 to 8 t ha−1 of dry phytomass and 1000 kg ha−1 to 1800 kg ha−1 of seeds. In this context, we planned an experiment to verify the tolerance and Ni accumulation capacity in Canavalia ensiformis. Our hypothesis was that increasing Ni concentration in the soil would not hinder the plant’s biomass production. We conducted a completely randomized experiment with five concentrations of Ni added to the soil and five replicates in a greenhouse during the vegetative stage. We evaluated the plant’s development, biomass production, and Ni accumulation in its organs. Our results demonstrated high tolerance to the metal, maintaining a biomass accumulation capacity of 68% of the dry mass in the soil with 277.8 mg kg−1 of Ni at the highest concentration tested, compared to plants in the control soil. Considering that under these conditions the plants obtained a biomass of 10 g of leaves and 15 g of roots, and a nickel accumulation capacity of 75.05 mg kg−1 in leaves and 102 mg kg−1 in roots, the total Ni accumulation in the plants reached 2.37 mg Ni/plant in the soil with 277.8 mg kg−1 of Ni. This soil Ni concentration would be lethal for most plants, and the metal concentration in the tissue exceeds the established limits for non-tolerant crops. With these results, this study aims to provide a foundation for improving the use of Canavalia ensiformis in phytoremediation.