Climate Change Affects How Soil Bacteria Breathe
A long-term experiment shows that climate shifts produce changes in soil bacteria functioning.
Understanding how climate change affects the way carbon cycles in and out of the soil is critical for predicting future changes in the carbon cycle, from ecosystem to global scales. This study capitalized on a long-term experiment in which mountain soils were transplanted between a hotter, drier lower elevation and a cooler, moist upper elevation to examine their response to climate change. The unprecedented 17-year length of this experiment is important because short-term experiments are not sufficient to adequately characterize all the ecosystem responses in slow-responding soils.
Soils store an enormous amount of carbon globally, and arid land soils are considered particularly sensitive to the effects of climate change. Little is known, however, about how these soils might react as the climate changes, and long-term experiments are extremely rare. Because humans depend on soils for stabilizing carbon against greenhouse gas emissions, cropland production, and a wide variety of other ecosystem services, understanding the effects of climate change on soil is important. Climate change can alter soil physical structure, the composition of microbial communities that reside in soil, amount of carbon that soil can store, and the respiration response.
A research team, including Department of Energy (DOE) scientists at Pacific Northwest National Laboratory (PNNL), PNNL’s Joint Global Change Research Institute, and a U.S. Department of Agriculture researcher at Washington State University, transplanted soils between two elevations of semi-arid Rattlesnake Mountain, located in eastern Washington state. They chose sites separated by 500 m of elevation with similar plant species and soil types, but very different temperature and rainfall patterns. This experiment was initiated in 1994; 17 years later the team resampled the transplanted soils and controls, measuring carbon dioxide (CO2) production, temperature response, enzyme activity, and bacterial community structure. After incubating the soils for 100 days, they found that transplanted soils (i.e., soils that had been moved between the two sites in 1994) respired roughly equal cumulative amounts of carbon as the nontransplanted soils. Soils transplanted from the hot, dry lower site to the cooler, wetter upper site exhibited almost no respiratory response to temperature—as the temperature rose, they barely responded—but soils originally from the upper cooler site respired at higher rates. However, the bacterial community structure of transplants did not change. These findings show that the climate changes experienced by the transplanted soils prompted significant differences in microbial activity, but no observed change to bacterial structure. These results support the idea that environmental shifts can influence soil carbon through metabolic changes in the soil microbial population, and that those microbes, responsible for the soil-to-atmosphere CO2 flux, may be constrained in surprising ways.
Pacific Northwest National Laboratory
This research was supported by DOE’s Office of Science, Office of Biological and Environmental Research (BER) as part of the Terrestrial Ecosystem Science program and the Signature Discovery Initiative at PNNL. Carbon analyses were performed at the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility sponsored by BER and located at PNNL.
Bond-Lamberty, B., et al. “Soil respiration and bacterial structure and function after 17 years of a reciprocal soil transplant experiment.” PLOS ONE 11(3), e0150599 (2015). DOI:10.1371/journal.pone.0150599.