Peatlands are important drivers of global climate because of their ability to store and release carbon and other organic matter. Despite the fact that boreal peatlands make up only 3% of Earth’s surface, they store about a third of all soil carbon. As land use practices and the planet’s climate continue to change, scientists are interested in understanding the chemistry and organization of these important areas.
In a new study, Tfaily et al. analyzed dissolved organic matter from a peat bog in northern Minnesota. In particular, the team was interested in whether changes to the water level in the bog would influence the chemistry of the organic matter within. They hypothesized that the oscillation between wet and dry states would accelerate the turnover of carbon, nitrogen, and sulfur in the soil.
Peat bogs, however, are not two-dimensional; their chemistry and constituents vary significantly with depth and the microbial communities that inhabit different layers of the soil. Scientists have classically recognized two distinct layers within the soil: The acrotelm is closer to the surface, and its chemistry is dictated mostly by plant life and the presence of oxygen; deeper down, the catotelm is anoxic, and most organic matter is stored as thick, brown, soil-like peat.
More recently, researchers have proposed a third layer, the mesotelm, which represents a transitional stage. This layer is highly dynamic and can contain oxygen or not, depending on the movement of water through the soil. This variability enables a wide range of microbes to inhabit the mesotelm and facilitate many different biological reactions and pathways.
To learn more about how soil microbes behave, the authors focused on this midlayer, which they defined as approximately 25 to 50 centimeters deep. Using a combination of molecular analysis tools—like mass spectrometry and excitation emission matrix fluorescence—combined with parallel factor analysis, the scientists constructed a detailed image of the kinds of organic compounds present in the mesotelm.
As the scientists looked deeper into the soil, they found similar types of organic material, but in later states of decay. The mesotelm boasted the highest rates of decay and the most diverse set of organic compounds. In line with their hypothesis, the authors suggest that water movement through pores in the soil is the main driver of the vertical stratification and depends on the larger ecosystem and regional water tables. The team concludes that the new work gives a better picture of how organic material evolves as it moves down through the soil, ultimately giving scientists a more complete picture of the planet’s ability to store and release carbon and other important molecules. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1002/2017JG004007, 2018)
—David Shultz, Freelance Writer