Environmental drivers define contrasting microbial habitats, diversity and functional redundancy in Lake Baikal, Siberia

Understanding how microbial communities respond to environmental change requires knowing the main drivers of their structure, diversity and potential resilience. Lake Baikal is the worlds most ancient, deep, voluminous, and biodiverse lake, holding 20 percent of unfrozen fresh water that is undergoing rapid warming. Despite its global importance, little is known about Baikals bacterioplankton communities and their drivers. In this extensive survey, we show that temperature, along with stratification, nutrients, and dissolved oxygen, but not geographic distance, define major microbial habitats and community similarity. Mixed layer and deep water communities exhibited contrasting patterns of richness, diversity and evenness, and comprised different cohesive modules in the whole Baikal OTU co-occurrence network. The networks small-world properties indicated likely resistance to perturbations but sensitivity to abundance changes of central, most connected OTUs. Previous studies showed Baikal water temperature rising by over 1.2{degrees}C since 1946, and this trend is predicted to accelerate. Because temperature emerged as the most significant predictor of the mixed layer community structure, we hypothesize that it is most likely to drive future community changes. Understanding how temperature and other abiotic factors structure microbial communities in this and other rapidly changing ecosystems will allow better predictions of ecosystem responses to anthropogenic stressors.