Co-cropping of <i>Bornmuellera emarginata</i>, <i>Lupinus albus</i> and <i>Imperata cylindrica</i>: a study of metal uptake interactions and nickel phytoextraction efficiency

Co-cropping of hyperaccumulators is still poorly understood, while associations between hyperaccumulators and other plant species may promote beneficial plant interactions and lead to increased metal phytoextraction from contaminated soils. The aim of this study was to evaluate the phytoextraction potential of the Ni-hyperaccumulator <i>Bornmuellera emarginata</i> in different co-cropping combinations with <i>Lupinus albus</i> and <i>Imperata cylindrica</i>. Plants were grown in ultramafic soil in a growth chamber for 45 days and Al, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn concentrations in roots and leaves were analyzed. Translocation factors were used to evaluate Ni phytoextraction. <i>Bornmuellera emarginata</i> accumulated foliar Ni at contents ranging from 3,410 to 6,500 mg kg⁻¹, with mean Ni concentrations in roots being seven times lower than in shoots (625–878 mg kg⁻¹). Co-cropping led to a reduction in biomass (25–62%) of <i>B. emarginata</i> and did not substantially increase Ni concentrations in shoots. To conclude, intercropping did not significantly enhance Ni phytoextraction by <i>B. emarginata</i>. However, <i>B. emarginata</i> and <i>L. albus</i> in co-cropping showed high translocations (&gt;1) for Co, Mn, Ni, and Zn, highlighting the potential of combining hyperaccumulators with other plant species as a viable strategy for phytoremediation of areas contaminated by multiple metals. The results of this show that <i>Bornmuellera emarginata</i> can be grown with other plants to remediate soils contaminated by multiple metals. The Ni phytoextraction efficiency of <i>B. emarginata</i> does not increase through co-cropping due to species competition and decreased biomass.