Contrasting resistance and resilience of the coupled oxic and anoxic components of an experimental microbial ecosystem

Understanding how microbial communities as key drivers of global biogeochemical cycles respond to environmental change remains a critical challenge in microbial ecology. In this study, we used phototrophic oxic-anoxic micro-ecosystems to understand how aerobic and anaerobic lake analog communities responded towards stressful light removal. Continuous oxygen measurements and four snapshots of full-length 16S rRNA sequencing were performed to detect responses of oxygen concentration, and of alpha and beta diversity. In the top layer, oxygen concentration decreased significantly under light limitation, but showed almost complete resilience after normal light conditions were restored, while the bottom layer remained anoxic throughout the experiment. Microbial communities, however, differed in their response behavior: alpha-diversity of the aerobic communities showed a delayed response after light conditions were restored, and their composition was not resilient during the duration of the experiment. In contrast, alpha-diversity of the anaerobic bottom water communities increased due to the stressor and was resilient. Beta-diversity changed significantly during light removal, showed resilience for the aerobic communities, but stayed significantly affected for the anaerobic communities. We conclude that whole-ecosystem responses and several time-points are needed to fully understand the impact of stressors on microbial ecosystems, since resistance/resilience can differ among and within abiotic and biotic ecosystem components.