The soils found in northern forests play an essential role in trapping carbon dioxide, which trees absorb and utilize for photosynthesis, preventing it from re-entering the atmosphere.
The soils of northern forests are key reservoirs that help keep the carbon dioxide that trees inhale and use for photosynthesis from making it back into the atmosphere.
However, a groundbreaking study conducted by Peter Reich from the University of Michigan reveals that, as our planet warms, the soil is releasing more carbon than the plants are contributing.
“This is concerning because it indicates that with global warming, soils will be returning some of their carbon to the atmosphere,” stated Reich, who directs the Institute for Global Change Biology at U-M.
“Overall, an increase in carbon loss is detrimental to the climate,” commented Guopeng Liang, the lead author of the research published in Nature Geoscience. Liang, who was a postdoctoral researcher at the University of Minnesota during the research, currently holds a postdoctoral position at Yale University and is an exchange fellow at the Institute for Global Change Biology.
By examining how rising temperatures influence carbon exchange within soil, scientists can gain insight into and predict shifts in our planet’s climate. Forests are significant carbon sinks, storing about 40% of the Earth’s soil carbon.
This crucial role has led to numerous research projects focused on how climate change impacts carbon flow from forest soils. However, very few studies have exceeded three years in duration, and most have only analyzed warming in either the soil or the air above it, but not both simultaneously, according to Reich.
In what is believed to be an unprecedented study of its kind led by Reich, researchers managed to regulate both soil and above-ground temperatures in an open-air setting without using enclosures. This study also spanned over twelve years.
“Our research is distinctive,” said Reich, also a professor at the U-M School for Environment and Sustainability. “It is by far the most realistic experiment of its type globally.”
The challenge of conducting such a complex and long-term study comes at a high cost. This research received funding from the National Science Foundation, the U.S. Department of Energy, and the University of Minnesota, where Reich is also recognized as a Distinguished McKnight University Professor.
Reich and Liang collaborated with fellow researchers from the University of Minnesota, the University of Illinois, and the Smithsonian Environmental Research Center.
The research team conducted their work at two locations in northern Minnesota, covering a total of 72 experimental plots and examining two warming scenarios against default conditions.
In one scenario, plots were maintained at 1.7 degrees Celsius above normal, while in the other, temperatures were 3.3 degrees Celsius higher (approximately 3 and 6 degrees Fahrenheit, respectively). They observed that soil respiration — the process responsible for releasing carbon dioxide — increased by 7% in the moderate warming plots and by 17% in the more intensive warming plots.
The carbon that is respired originates from the metabolic activities of plant roots and soil microorganisms that feed on available carbon sources: sugars and starches released from roots, decomposing plant matter, soil organic material, and other living or dead microorganisms.
“Microbes function similarly to humans. Some of what they consume is released back into the atmosphere,” noted Reich. “They employ the same metabolic process as we do to exhale CO2 back into the air.”
While the researchers found that carbon dioxide emissions rose in higher temperature plots, the increase was not as significant as it could have been.
The experimental design also took into account soil moisture, which tends to decline in warmer environments as plants and soils lose water more quickly. Nevertheless, microbes thrive in moister soils, and the dryness of the soil in warmer conditions limited respiration.
“The main takeaway is that forests are likely to lose more carbon than we would prefer,” stated Reich. “However, this loss may not be as severe due to the drying effects we’re observing.”
