Background/Question/Methods Soils contain immense diversity, support terrestrial ecosystem functions, and contain most of Earth’s terrestrial C. However, soils and the C they store are under threat as they face numerous anthropogenic pressures. Understanding how soils will respond to multiple stressors is critical for maintaining biodiversity and function. Here, we examined how introductions of low and high doses of the common livestock antibiotic Monensin shape soil communities, and how these effects are exacerbated by shifts in soil temperature. Soils were collected from native uncultivated prairie in Northern Idaho, and maintained in microcosms that were incubated at 15, 20 or 30oC. Each microcosm was treated with high doses, low doses or no antibiotics. Soil respiration was measured bi-weekly for 3 weeks to capture how antibiotics and temperature shape CO2 emissions. After our 21 day incubation, soil microbial communities were monitored with amplicon sequencing and qPCR to examine changes in community composition, microbial network connectivity and fungal:bacterial ratios. We also examined soil nutrient characteristics, including bioavailable C, microbial biomass C and N, pH and C-use efficiency, in order to determine how multiple stressors shape soil nutrient stoichometry.
Results/Conclusions Antibiotics and temperature disrupted soil microbial communities and function. When antibiotics were combined with higher temperatures, bacterial network structure collapsed, allowing for increased fungal dominance and decreased microbial C:N. Independent of temperature, antibiotics decreased bacterial diversity, abundance, total extractable N and microbial efficiency, while increasing bioavailable C. Higher temperatures independently homogenized fungal community composition, decreased dissolved organic C and increased soil respiration rates. These results demonstrate that soil stress response depends on the stressor and that unique shifts in composition and function will occur as soils encounter multiple congruent stressors. We also found that both the independent and interactive effects of temperature and antibiotics can lead to decreases in soil ecosystem stability and resilience, while also making long-term C storage more difficult in soils. Combined, these results show that interacting stressors can push soil communities into novel assemblages with altered function. Therefore, efforts to preserve soil health and increase C storage in soils must consider multiple anthropogenic stressors.