Stream benthic microbial communities play a key role in energy transfer and biogeochemical cycling. Climate change is expected to increase the intensity and duration of disturbance in headwater stream ecosystems, resulting in higher temperatures and intensified hydrologic regimes, including wet-dry cycles. The impacts of single disturbance types are relatively well-studied in streams; however, we lack understanding of how stream microbes respond to the combined stressors of warming and drying. While multiple stressors are generally thought to act additively to suppress ecological structure and function, emerging evidence suggests that long-term warming may induce compensatory responses that promote resilience to drying through physiological adaptation and shifts in community structure. Here, we outline a plan to investigate whether long-term warming promotes resilience in the structure and function of microbial communities to intense drought.
We are conducting a large-scale temperature and drying manipulation to assess microbial responses to concurrent stressors. Eight experimental outdoor flumes at ambient (20°C) and eight at warmed (+5°C) temperatures (University of Birmingham, UK) were inoculated with biofilms from nearby streams in July 2024. We plan to simulate an intense drought by gradually reducing flow for one month in June 2025, resulting in a 1-month total dry-down. We will then re-initiate flow and follow ecosystem recovery for 3 months. To assess community change, we will sample biofilms and the water column using 16S rRNA metabarcoding to identify amplicon sequence variants. We will assess functional responses from rates of community (RC) respiration using the resazurin-resorufin system and by measuring source-specific carbon utilization from EcoPlates. We expect warming to increase RC and simplify microbial community structure, and that microbial community function and structure will recover faster post-drought in warmed flumes. Results from this project will inform how stream biofilms respond to concurrent stressors, and improve understanding of ecosystem response to a changing climate.