Effects of Nutrient Limitation on Antarctic Microbial Community Diversity, Composition, and Interactions: A Cryoconite Microcosm Study

Dry, harsh, nutrient-limited environments such as the McMurdo Dry Valleys, Antarctica, may be particularly susceptible to changes in nutrient availability, demonstrating strong deterministic community assembly processes shaping communities within an ecosystem largely dominated by stochastic processes. Utilizing previously characterized cryoconite hole sediments from Canada Glacier in Taylor Valley, Antarctica, we carried out a microcosm study to examine the effects of alleviating nutrient limitation. Using a factorial experiment of nitrogen and phosphorus, we characterized the impact of nutrient additions on community growth, richness, composition, and interactions. We identified cascading effects where the addition of nutrients led to increased microbial phototroph growth (e.g., Chlorococcum) and abundance of higher trophic-level microbial and invertebrate predators (e.g., cercozoans and rotifers). Nutrient additions did not influence community richness but altered the composition and interactions within communities. Overall, nutrient additions promoted larger community networks dominated by positive inter-domain interactions, except for phosphorus additions, which resulted in communities dominated by negative interactions. Regardless of the type of interactions, all networks were dominated by cross-domain interactions. Unlike additions in other ecosystems, which resulted in changes to species richness, we show that nutrient additions in extreme oligotrophic environments can alter community composition and complexity, while maintaining richness.