Pharms on farms: Variable impacts of veterinary pharmaceuticals on arbuscular mycorrhizal structure and function

Intensive agricultural practices have degraded soils, reducing their ability to support crop production. One concept that could help resolve these issues by supporting soil health, or "the ability of soil to sustain the productivity, diversity, and environmental services of terrestrial ecosystems", is circular agriculture. This includes the reuse of waste products, such as manure, as soil amendments. Unfortunately, however, the reuse of manures can inadvertently lead to chemical migration into agricultural soil, resulting in frequent detection of chemicals that would otherwise not be found in soils, such as veterinary pharmaceuticals. Some of these have been found to accumulate in plant tissues and negatively impact plant health. Despite having effects on plant health, there have not been many studies investigating the impact of human and veterinary pharmaceuticals on soil microbial function, including arbuscular mycorrhizal (AM) fungi, highlighting a key gap. AM fungi are ubiquitous soil microbes that form associations with most land plant roots and greatly contribute to soil nutrient cycling and plant nutrient acquisition. Because of these functions, there is increasing interest in exploiting AM fungal function in agriculture to reduce chemical fertiliser inputs. We addressed this critical knowledge gap by assessing the impacts of three veterinary pharmaceuticals, doxycycline (DOX; antibiotic), sulfamethoxazole (SMX; antibiotic), and flubendazole (FLUB; anthelminthic, an anti-parasitic), on the structure and function (C-for-nutrient exchange) of the arbuscular mycorrhizal associations in the dwarf runner bean (Phaseoluscoccineus 'Hestia') using radio- and stable-isotope tracers in soil-based systems. Additionally, we evaluated impacts of exposure to the veterinary pharmaceuticals on the root and soil microbiome (bacteria and fungi) using DNA amplicon sequencing.