Seasonality and bacterial community assembly processes dominate prairie ecosystem service disruption during invasion

Invasive plants alter soil microbial communities and ecosystem services reducing the Earth's carrying capacity for humans. Many ecosystem services are underpinned by soil microbial communities, and these communities arise from assembly processes that are likely altered by invasion. We evaluated the hypothesis that invasive effects on grassland ecosystem services arise from changes in microbial community assembly processes caused by invasion. We sampled 515 plots at a native Rough Fescue prairie undergoing invasion by nine invasive species of which smooth brome (Bromus inermis) is a dominant member. Each week, for 26 weeks, we monitored invasion effects on vascular plant communities, ecosystem services, as well as bacterial and fungal community structures. Invasive effects on ecosystem services interacted with seasonal (plant green-up, peak biomass, and plant senescence) effects and consistently disrupted ecosystem service provision. Invasion increased heterogenous selection in fungal communities but otherwise had minor effects on assembly process. Only ∼20% of community composition could be ascribed to deterministic filters which hindered our ability to conclusively link invasion to assembly processes. Assembly processes explained changes in ecosystem services with bacterial assembly accounting for 2.5% of food, 4% of climate, 9% of conservation and 5.5% of fertility services. Fungal communities were less consistent in their effects on ecosystem services with only food (3%) and water (4%) services influenced by fungal assembly. After seasonality (27%), bacterial assembly processes (4%) accounted for the largest effect on ecosystem services, overshadowing invasion (2%) and fungal assembly (2%). At this 130-hectare site, after seasonal effects, bacterial assembly processes had the largest effect on ecosystem services with plant invasion placing a distant third.