Large and interacting effects of temperature and nutrient addition on stratified aquatic ecosystems-results from a model micro-ecosystem

Aquatic ecosystems are often stratified, with cyanobacteria in oxic layers and phototrophic sulfur bacteria in anoxic ones. Changes in stratification caused by global environmental change are an ongoing concern. Increasing understanding how such aerobic and anaerobic microbial communities, and associated abiotic conditions, respond to multifarious environmental changes is an important endeavor in microbial ecology. Insights can come from observational and experimental studies of naturally occurring stratified aquatic ecosystems, from theoretical models of ecological processes, and from experimental studies of replicated microbial communities in the laboratory. Here we demonstrate a laboratory-based approach with small, replicated, and liquid dominated Winogradsky columns, with distinct oxic/anoxic strata in a highly replicable manner. Our objective is to apply simultaneous global change scenarios (temperature, nutrient addition) on this micro-ecosystem to report how the microbial communities (full-length 16SrRNA-seq.) and the abiotic conditions (O2, H2S, TOC) of the oxic/anoxic layer responded to these environmental changes. Composition of the strongly stratified microbial communities was greatly affected by temperature and by the interaction of temperature and nutrient addition, demonstrating the need of investigating global change treatments simultaneously. Especially phototrophic sulfur bacteria dominated the water column at higher temperatures, and may indicate the presence of alternative stable states. We show that the establishment of such a micro-ecosystem has potential to test global change scenarios in stratified eutrophic limnic systems.