Abstract
Uncovering microbial response to salinization or desalinization is of great importance to understanding of the influence of global climate change on lacustrine microbial ecology. In this study, to simulate salinization and desalinization, sediments from Erhai Lake (salinity 0.3–0.8 g/L) and Chaka Lake (salinity 299.3–350.7 g/L) on the Qinghai–Tibetan Plateau were transplanted into different lakes with a range of salinity of 0.3–299.3 g/L, followed by in situ incubation for 50 days and subsequent geochemical and microbial analyses. Desalinization was faster than salinization in the transplanted sediments. The salinity of the transplanted sediment increased and decreased in the salinization and desalinization simulation experiments, respectively. The TOC contents of the transplanted sediments were lower than that of their undisturbed counterparts in the salinization experiments, whereas they had a strong negative linear relationship with salinity in the desalinization experiments. Microbial diversity decreased in response to salinization and desalinization, and microbial community dissimilarity significantly (P < 0.01) increased with salinity differences between the transplanted sediments and their undisturbed counterparts. Microbial groups belonging to Gammaproteobacteria and Actinobacteria became abundant in salinization whereas Bacteroidetes and Chloroflexi became dominant in desalinization. Among the predicted microbial functions, hydrogenotrophic methanogenesis, methanogenesis through CO2 reduction with H2, nitrate/nitrogen respiration, and nitrification increased in salinization; in desalinization, enhancement was observed for respiration of sulfur compounds, sulfate respiration, sulfur respiration, thiosulfate respiration, hydrocarbon degradation, chemoheterotrophy, and fermentation, whereas depressing was found for aerobic ammonia oxidation, nitrate/nitrogen respiration, nitrification, nitrite respiration, manganese oxidation, aerobic chemoheterotrophy, and phototrophy. Such microbial variations could be explained by changes of transplantation, salinity, and covarying variables. In summary, salinization and desalinization had profound influence on the geochemistry, microbial community, and function in lakes.
Highlights
Lakes are distributed globally and respond sensitively to regional and/or global environmental changes (Adrian et al, 2009; O’Reilly et al, 2015)
This finding could be ascribed to the following fact: in the salinization simulation experiments, osmotic stress resulted in salt-in and water-out, and dry microenvironment was formed in the caged sediments, which did not avail to further exchange water and salt between inside and outside of the cages; whereas an opposite water–salt exchange trend took place in the desalinization simulation experiments, and water–salt exchange became easier as desalinization proceeded (Brown, 1976, 1990; Oren, 2008)
Salinization and desalinization had strong effects on sedimentary geochemistry, microbial community compositions, and functions in the transplanted sediments, and the desalinization process was faster than salinization
Summary
Lakes are distributed globally and respond sensitively to regional and/or global environmental changes (Adrian et al, 2009; O’Reilly et al, 2015). Lake salinization and desalination are growing environmental problems caused by both human activities (Dugan et al, 2017) and climate changes (Fedotov et al, 2013). Continuous anthropogenic perturbations and climate changes (e.g., drying, humidification) often lead to lake surface area shrinkage or enlargement, resulting in salinization (i.e., salinity increase) (Micklin, 2007; Guo et al, 2015) or desalination (i.e., salinity decrease) (Schulz, 2000; Fedotov et al, 2013), respectively. Little is known about how salinization and desalinization affect microbial community compositions and their metabolic functions in lakes
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