Nickel tolerance and phytoremediation potential of the aquatic plant Lemna minuta and the cyanobacterium Trichormus variabilis in monoculture and consortium

One of the main threats to aquatic conservation is heavy metal pollution, with nickel (Ni) among the most significant contaminants. The Ni tolerance and remediation potential of Lemna minuta (vascular plant) and Trichormus variabilis (cyanobacterium) in contaminated water were investigated. The phytotoxic effects of nickel sulfate (NiSO4·7 H2O; 6.47 mg/L) on these two species, were assessed after 7- and 14-days exposure by measuring morphological changes, growth (fresh weight) and key physiological parameters (chlorophyll, malondialdehyde, protein content and catalase activity). The ability of L. minuta and T. variabilis to remove Ni was compared in both monoculture (single species) and consortium (mixed species) by measuring the reduction in Ni concentration in the culture medium. Nickel exposure induced phytotoxic effects in both species, as shown by decreases in fresh weight, chlorophyll and protein content, and increases in malondialdehyde content and catalase activity. These effects were more pronounced in monocultures, particularly in T. variabilis, compared to consortia. Lemna minuta exhibited good Ni tolerance and remediation capacity, removing 75 % and 86 % of the metal from the solution after 7 and 14 days, respectively. Trichormus variabilis removed 36 % and 27 % of the Ni after the same exposure time. Consortia exhibited high Ni removal, reaching 80 % and 90 % after 7 and 14 days, but this was not statistically different to L. minuta monocultures. These results demonstrate the potential of L. minuta in the remediation of Ni-contaminated waters and suggest that consortia might enhance the tolerance and viability of both species under Ni-stress.