Per- and polyfluoroalkyl substances (PFAS) can impact plant growth, while how the symbiosis of arbuscular mycorrhizal fungi (AMF) would affect the response of plant performance to PFAS contamination remains entirely unknown. To address this gap, we conducted an eight-week pot experiment to investigate the function of AMF in plant response to perfluorooctanoic acid (PFOA) using spring onion (Allium cepa) as phytometer. At harvest, we measured whole-plant performance (including growth, root morphology and mycorrhizal association) and soil parameters (pH and litter decomposition rate) as affected by PFOA and AMF inoculation. Our results showed that PFOA reduced the AMF colonization rate, frequency of arbuscules and vesicles. It also negatively affected root traits including root biomass, total length, average diameter, and root tissue density, while positively affecting specific root length and surface area. Moreover, PFOA significantly decreased leaf biomass, maximum height, and total biomass, but did not affect root/shoot ratio, soil pH, and litter decomposition. The inoculation of AMF reduced the negative effect of PFOA on root diameter and the positive effects on specific root length and surface area. It also increased the total root length, but this effect was neutralized by PFOA. Our results suggest that AMF inoculation alters the resource allocation strategies of plants under PFOA stress, favoring shoot growth at the expense of roots. This study provides evidence that AMF inoculation enhances plant resistance to environmental stressors and highlights the need to explore its interactions with plants and pollutants like PFAS.
