September 01, 2020

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Soil Bacterial Responses to a Thawing Arctic: A Microbial Awakening

Soil Bacterial Responses to a Thawing Arctic: A Microbial Awakening

Cross section of a permafrost-affected soil profile illustrating soil layers analyzed by the study.
[Image Credit: Image courtesy of Argonne National Laboratory.]

The Science

Bacteria living in soil respond to environmental conditions, such as moisture, temperature, and soil chemistry (e.g., pH, nutrients, and minerals). In the Arctic, global warming is causing permafrost (continuously frozen ground) to thaw and bacterial communities to change. Researchers investigated how warming affects bacteria in different soil layers sampled from tundra sites in northern Alaska. When permafrost thawed, bacteria that grow quickly in nutrient-rich environments increased, while bacteria that grow slowly and survive on limited resources decreased. In contrast, bacterial responses to warming of surface soil layers that thaw every summer were less drastic and more influenced by soil chemistry.

The Impact

Soil microbes, including bacteria, regulate many processes essential to sustaining life on Earth, including carbon and nutrient cycling. Yet, scientists have limited understanding of how environmental changes affect soil microbial communities and their ability to perform vital ecosystem functions. This study revealed that permafrost microbial communities can respond to Arctic warming by rapidly shifting bacterial abundances to maximize functional strategies that take advantage of short-term resource changes caused by abrupt thawing and higher temperatures. It also suggests that soil chemistry will likely play a large role in shaping the structure and function of bacterial communities over the long-term.

Summary

Arctic soils hold a substantial portion of the global carbon pool because cold temperatures have limited microbial decomposition of soil organic matter (SOM) and carbon mineralization for millennia. Yet, warming is occurring much faster in the Arctic than in other regions. Understanding how soil microorganisms respond to warming-induced changes—in both the seasonally thawed active layer and underlying permafrost—will inform efforts to project the fate of soil carbon in the Arctic.

Upper permafrost and two contrasting active layer soils (organic and mineral) were sampled at four tundra sites with differing soil properties, incubated at five temperatures ranging from −1°C to +16°C, and analyzed for chemical composition and bacterial community structure. Bacteria known to thrive in carbon- and nutrient-rich environments responded positively when permafrost was incubated above 0°C, reflecting increased access to labile SOM upon thaw. While bacterial community structure was driven primarily by site and soil layer type, soil chemistry data improved predictive models. Although the largest pre- to post-incubation shifts in bacterial abundance occurred in permafrost, correlations between SOM chemistry and bacterial abundance were far greater in active layer soils, suggesting annual thawing produces a more stabilized community that is attuned to its specific environment.

Principal Investigator

Julie Jastrow
Argonne National Laboratory
jdjastrow@anl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Earth and Environmental Systems Sciences Division, under contract DE-AC02-06CH11357.

Related Links

References

Ricketts, M. P., R. Matamala, J. D. Jastrow, and D. A. Antonopoulos et al.. "The effects of warming and soil chemistry on bacterial community structure in Arctic tundra soils". Soil Biology and Biochemistry 148 107882  (2020). https://doi.org/10.1016/j.soilbio.2020.107882.