Field-Relevant Soil Concentrations of Fluopyram: Effects on Cover Crop Establishment and Biomass, Root Architecture, Earthworms, Springtails, and Decomposition

Abstract

Fluopyram is a broad-spectrum fungicide and nematicide used in foliar sprays and seed treatments. Despite its low volatility and moderate solubility, it is frequently detected beyond application sites in air, soil, and water. As a per- and polyfluoroalkyl substance (PFAS)-class “forever chemical”, its off-site presence raises ecotoxicological concerns. We conducted a 61-day greenhouse experiment to assess the effects of fluopyram residues in soil (0, 0.02, 0.04, and 0.78 mg kg−1 soil) on two cover crop species (Italian clover, Trifolium incarnatum; cornflower, Centaurea cyanus), earthworms (Lumbricus terrestris), springtails (Folsomia candida), and litter decomposition. Measured endpoints included plant establishment, growth, biomass, photosynthetic efficiency, root architecture, soil fauna activity, and litter breakdown. Responses were species-specific and did not exhibit clear dose–response relationships. Height growth in Italian clover and cornflower showed significant treatment × date interactions, whereas establishment and biomass production remained unaffected. In Italian clover, root diameter increased with fluopyram concentration, while root length and volume showed non-significant trends. Cornflower roots exhibited fewer crossings at higher concentrations but were otherwise unaffected. Photosynthetic efficiency remained unchanged in both species, although it tended to decrease modestly in cornflower at the highest concentration. Springtail surface activity density was generally influenced by fluopyram, with significant treatment × date interactions at 0.04 and 0.78 mg kg−1. Earthworm effects were inconclusive due to low survival rates. Neither litter decomposition rate nor stabilization factor was affected. Our results show that fluopyram residues in soil can induce subtle, species-specific effects in non-target organisms. However, long-term studies are needed to clarify how this highly persistent active ingredient and its degradation products accumulate in soils and interact with co-occurring pesticides, thereby improving ecological risk assessments.