Enhanced Nickel Uptake in Mixed Plant Communities of Hyperaccumulator and Non‐Hyperaccumulator Species Under Nickel Stress

ABSTRACT Biodiversity loss can negatively affect ecosystem functioning, yet its influence on processes related to metal uptake remains poorly tested. Here, we investigate for the first time how species richness affects biomass production and nickel phytoextraction under serpentine stress using endemic plants occurring in Mediterranean ecosystems. Monocultures and bicultures of Odontarrhena lesbiaca (nickel hyperaccumulator) and Alyssum xiphocarpum (non‐hyperaccumulator) were grown on three substrates representing a gradient of increasing stress: peat, a peat‐serpentine mixture, and pure serpentine soil. Serpentine soil had the highest total nickel concentration, and aboveground biomass generally declined with increasing soil nickel levels. Across all substrates, bicultures increased soil nickel bioavailability and total aboveground biomass and enhanced the phytoextracted nickel mass by an average of 29% compared to monocultures. The hyperaccumulator had higher tissue nickel concentrations, while the presence of the non‐hyperaccumulator enhanced phytoextraction in mixtures, suggesting facilitative species interactions that promote nickel mobilization and uptake in line with the stress‐gradient hypothesis. These findings indicate that combining hyperaccumulator and non‐hyperaccumulator species can enhance nickel phytoextraction in metal‐stressed soils, offering a promising biodiversity‐based approach to agromining and remediation of metal‐polluted environments.