Maladaptive Soil Microbes Warn of Rocky Road Ahead
A 17-year-long experiment shows that climate shifts change how well the underworld of soil bacteria functions
Moving Microbes The soil samples taken from near the top of Rattlesnake Mountain in Eastern Washington were transplanted to the prairie 500 meters below. Similar samples from the prairie were transplanted to the mountain site. This habitat swap showed that even after 17 years, the transplants retained remarkably similar soil microbial behavior—as if they had never been moved. Enlarge Image.
Results: Climate warming may have long-term effects on soil, and how well the microbial residents within it behave, found researchers at Pacific Northwest National Laboratory. In particular, their ability to digest carbon, an activity scientists call respiration. A new study published in the journal PLoS ONE shows that even when the microbes' structure has not changed, their level of activity does. As primary indicator of healthy, active soil, respiration is vital for maintaining productive growth in soil and digesting carbon and other elements it contains.
"Soil is the major buffer system for environmental changes, and the microbial community is the basis for that resilience. If the microbial community is not as resilient as we had assumed, then it calls into question the resilience of the overall environment to climate change," said Dr. Vanessa Bailey, PNNL soil microbiologist and co-author of the study.
Why It Matters: Air, sunlight, water, dirt. Humans rely on these basic elements to nurture the environment necessary for life. There is also an underworld of microorganisms, unseen by the naked eye, but just as vital. While we depend on soil to grow crops, sustain forests, and control erosion, soil also provides a wide variety of other vital ecosystem services. Soil bacteria, fungi and other microbes are constantly at work to convert carbon and other elements into carbon dioxide and other gases and expel them into the atmosphere. This is potentially the most climate sensitive activity performed within soil. But will these microbes perform as well in a warmer climate?
Soils store an enormous amount of carbon globally, and arid land soils—a very dry environment—are considered particularly sensitive to the effects of climate change. Little is understood, however, about how these soils might react, and long-term experiments involving soil are extremely rare. Researchers believe that a study of this length of time will be extremely useful in calibrating climate models with real-world data.
Methods: Seventeen years ago, researchers set up the study by moving samples of soil down a mountainside in Eastern Washington State by 500 meters to a warmer, drier climate. Other samples were moved up 500 meters to a cooler, moister climate. After 17 years, the research team analyzed the make-up of the microbial communities, the enzyme activity, water retention ability, bacterial community structure and its rates of respiration, a key measurement that tells how quickly microbes convert carbon in the soil into carbon dioxide.
The team found less adaptability than they expected, even after 17 years. While the microbial make-up of the samples did not change much at all, the microbes in both sets of transplanted soils retained many of the traits they had in their "native" climate, including to a large degree their original rate of respiration.
"We can't assume that soils will respond to climate changes in the ways that many scientific models have assumed," said Dr. Ben Bond-Lamberty, lead author of the study and a terrestrial ecologist working at PNNL's Joint Global Change Research Institute (JGCRI). JGCRI is a partnership between PNNL and the University of Maryland, located in College Park, Md.
For more information, read PNNL news release "Microbes may not be so adaptable to climate change."
What's Next? Long-term experiments, such as the one used here, are critical to estimate and understand the effects of climate change on relatively slow-responding soils. The researchers will continue to couple field, lab, and modeling experiments to apply the knowledge gained here in broader contexts.
Sponsors: This research was supported by the Department of Energy, Office of Science, Biological and Environmental Research (BER) as part of the Terrestrial Ecosystem Sciences Program and the Signature Discovery Initiative at the Pacific Northwest National Laboratory, a Laboratory Directed Research and Development program.
User Facility: Carbon analyses were performed at EMSL, the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility sponsored by the BER and located at PNNL.
Research Team: Ben Bond-Lamberty, Harvey Bolton, Sarah Fansler, Alejandro Heredia-Langner, Chongxuan Liu, Lee Ann McCue, and Vanessa Bailey, PNNL; Jeffrey Smith (deceased), Washington State University.
Research Area: Climate and Earth Systems Science
Reference: Bond-Lamberty B, H Bolton, S Fansler, A Heredia-Langner, C Liu, LA McCue, J Smith, and V Bailey. 2016. "Soil Respiration and Bacterial Structure and Function after 17 years of a Reciprocal Soil Transplant Experiment." PLoS ONE 11(3): e0150599. DOI:10.1371/journal.pone.0150599