Assisting nickel agromining using sustainable amendments

One of the challenges of agromining is the adoption of more environmentally-friendly solutions to improve plant biomass yields and Ni concentrations in plants. Here, we focused on four sustainable solutions for optimizing nickel phytoextraction by the hyperaccumulator Odontarrhena chalcidica: a biostimulant, another biostimulant/plant defense stimulator, artificial root exudates, and a biodegradable metal chelator. Their effects on the growth and physiology of O. chalcidica, on Ni phytoextraction capacity, on physicochemical soil characteristics, and on the diversity of rhizosphere and endophytic bacteria were compared to a conventional mineral fertilizer. A 5-month pot experiment was carried out with O. chalcidica growing on an ultramafic soil. Element concentrations in both soil and plant were measured. Moreover, numerous compounds were analyzed (photosynthetic pigments, malondialdehyde, flavonoids, free amino acids, and starch). We also characterized rhizosphere and endophytic bacterial communities associated with this hyperaccumulator. Biostimulants appeared to be a promising way of improving Ni concentration in shoots and plant biomass production, and showed a positive effect on bacterial richness and diversity. In contrast, our experiments did not show that artificial exudates and mineral fertilizer had a positive effect on Ni phytoextraction. Finally, the biodegradable chelator had no significant effect. The use of sustainable amendments into a Ni agromining system improved both plant biomass and Ni yields, in comparison to mineral fertilization. Thus, improving agromining by replacing mineral fertilizers would be an eco-efficient strategy.