Rare earth elements in agroecosystems: a review of plant defenses and cascading effects on insect herbivores and pollinators

Rare earth elements (REEs), widely used in electronics, energy, and agriculture, are increasingly released into the environment, raising concerns about their ecological impacts. Although not essential nutrients, REEs can modify plant physiology by mimicking calcium, altering ionomes, and modulating jasmonic acid, salicylic acid, and redox signalling. At low concentrations, they stimulate growth and stress tolerance, whereas higher exposures impair photosynthesis and nutrient uptake. These plant-level shifts cascade to above- and belowground invertebrates through changes in tissue quality, secondary metabolites, and volatile organic compounds, with emerging evidence of altered growth, survival, fecundity, and behaviour. Pollinators encounter REEs via nectar, pollen, dust, and water, where sublethal effects on physiology and biochemistry raise concerns for pollination services. Yet, most studies rely on short-term laboratory assays at unrealistically high concentrations. We highlight pathways of exposure, organismal responses, and food-web implications, and identify research priorities to assess REEs as hidden modulators of agroecosystems.