The ground beneath your feet contains regarding 2,500 gigatonnes of carbon, which is regarding three times the amount of carbon in our atmosphere and four times more than is stored in any living thing – trees, ants, whales and humans included – on our planet. planet. .
Despite this, the dynamics that govern soil carbon cycles are less well understood than the dynamics of other carbon stocks.
Now, researchers at Virginia Tech, in collaboration with scientists from the U.S. Department of Agriculture Forest Service, the National Science Foundation’s National Ecological Observatory Network (NEON), and other universities, offer a new perspective on these processes, revealing that moisture is a key driver in the regulation and sequestration of soil carbon stocks.
“We demonstrate, at the molecular level, that there is a big difference in how carbon in the soil is cycled between moist and arid soil systems,” said Brian Strahm, a professor in the Department of Forest Resources at the College of natural resources and the environment. and Environmental Conservation and a Principal Investigator on the grant that funded this research. “This is useful for allowing us to imagine two fundamentally different models of how carbon is concentrated and moves through the soil.”
These findings, published in the journal Proceedings of the National Academy of Sciences, contradict the group’s original expectations of what factors make soil effective for carbon sequestration.
“The big takeaway is that most of the things we thought we knew regarding soil carbon were wrong,” said Kate Heckman, a Forest Service biology researcher and lead author of the paper. “Our initial hypothesis centered on the importance of certain types of soil minerals that we assumed were important in carbon persistence, or how long carbon stays in the soil. We also thought temperature patterns at the sites would be a powerful regulator of carbon age, but we didn’t see the signals we expected to see associated with temperature or soil mineralogy.”
The extent of a continent of soil samples
To better understand the interrelationship between soil carbon and moisture, the group used core samples collected by NEON, an observation network that strives to collect long-term ecological data on the northeastern continent. American to better understand how ecosystems evolve.
As part of this effort, the facility installed hundreds of buried sensors to monitor ground dynamics. The meter-deep cores they dug – 400 of which were used in this study – gave the researchers a critical snapshot of thousands of unique soil “horizons” or layers of soil that exhibit different characteristics in depending on age and composition.
“Opening the cores was like seeing different parts of the country through an 8 x 200 millimeter snapshot of the ground,” said Adrian Gallo, who was commissioned to do many of the initial core analyzes and recently completed his doctorate. in soil science at Oregon State University. “It wasn’t uncommon to open the cores and think, ‘What’s going on here with the colors and the rocks and the roots?’ And then I should look at aerial images, topographic maps and soil descriptors of nearby places to help me understand the history of the landscape.”
From these core samples, the researchers used a combination of radiocarbon and molecular composition analyzes to reveal the relationship between the abundance and persistence of carbon in the soil and the availability of moisture in the region where the samples were taken.
“I focused specifically on how soil carbon decomposition might differ across large-scale climate gradients,” said Assistant Professor Angela Possinger, who studies soil science in the School of Plant and Environmental Sciences. from the College of Agricultural and Life Sciences. “We ended up dividing the sites into systems that can be grouped into ‘wet’ and ‘arid’ climates, which goes along with many other differences in ecosystem and soil properties. This division ended up helping us to better describe the differences in decomposition rates. across the United States”
Associate Professor Brian Badgley, also from the School of Plant and Environmental Sciences, helped interpret the data, particularly considering the biological implications of these findings. He said the research fills a knowledge gap in our understanding of large-scale soil microbiology.
“The gap between how we analyze soil microbial communities using samples of just a few grams, and the regional and global scales where the carbon cycle is often considered, presents an immense challenge” , Badgley said. “The identification of continental subsystems in this work provides an exciting conceptual framework for how we can consider microbial processes across a broad landscape.”
Lead author Heckman, who worked with researchers at Michigan Technological University, hopes scientists will build on these findings. One future area of investigation she suggests would be field and cropland manipulation studies, which would allow scientists to see first-hand how moisture change affects soil carbon processes.
“Soil organic carbon is considered one of the most promising carbon capture and sequestration approaches we have, and understanding the role moisture plays in this process is key to helping us realize this potential. ” said Heckman. “I hope this study will encourage much of our scientific community to examine the role of humidity in the Earth’s carbon cycle.”
Strahm emphasizes that it is essential for scientists studying global carbon to understand that different soil systems require different models to predict changes in soil carbon stocks.
“We can’t use the contemporary vision and model to predict how these soil systems will change in the future,” said Strahm, who is an affiliate professor at the Global Change Center. “When we expect the systems to get wetter or drier, we move them from one bucket to another. But this kind of change has all sorts of implications, so an appreciation of two distinct systems will be a critical conceptual leap.”
