Synergy in Soil
Researchers look to the soil to deal with rising CO2 levels
Three researchers at Pacific Northwest and Argonne National Laboratories have made a significant step in describing the complex interactions involved in using soil to store carbon, an important player in global climate change. As atmospheric carbon dioxide levels rise, short- and long-term solutions are needed to store carbon removed from the air. Soil provides an abundant, readily available storage option—one designed by nature to hold carbon removed from air by plant photosynthesis.
"Creating short-term solutions, for say the next 50 to 75 years, is critical to buy the world time to come up with greener energy sources and better ways to sequester carbon," said Vanessa Bailey, the team's microbiologist at PNNL.
Bringing together expertise and resources in soil physics, microbiology and chemistry, the researchers described the two major mechanisms they believe control the turnover of carbon in soil. By manipulating these mechanisms, the retention of carbon by soil can increase.
The first mechanism involves chemical alteration driven by the types of minerals present and by the diverse and abundant microbial community, which both stabilizes and releases carbon. Many fungi consume carbon in the soil, converting it into a more stable form; however, a portion of the consumed carbon is unavoidably respired as carbon dioxide to the atmosphere. While bacteria also contribute to carbon stabilization, they tend to use carbon less efficiently than fungi and to produce residues that are more readily degraded.
Researchers recently made a significant step in in describing the complex interactions involved in using soil to store carbon, an important player in global climate change. Soil provides an abundant, readily available storage option—one designed by nature to hold carbon removed from air by plant photosynthesis.
The second mechanism involves the physical properties of the soil itself. Soil structure, the arrangement of soil particles and the pore spaces between them, helps determine if a soil will hold carbon for decades or release it quickly. When present in certain types of soil pores, the carbon can be protected from microorganisms, oxygen, and other factors that could cause it to be released.
"We were able to clearly identify these mechanisms because we looked at the soil from a variety of scientific perspectives," said Jim Amonette, the team's soil chemist also at PNNL.
To increase the persistence of carbon in soil, the research team provided several recommendations. Encouraging the fungal community and increasing carbon inputs from roots by minimizing tillage and planting perennial crops enhances soil structure and increases carbon storage times. Managing water is also important. Cycling between moist and dry conditions, and avoiding long periods at either extreme, promotes chemical transformations to more recalcitrant forms of carbon.
This research is part of the U.S. Department of Energy Consortium for Research on Enhancing Carbon Sequestration in Terrestrial Ecosystems (CSiTE) which also includes researchers at Oak Ridge National Laboratory.
In the near future, these researchers plan to develop methods to screen soils for carbon sequestration potential based on their microbial communities. On the horizon, researchers are looking at amending soil with highly persistent "biochar" that is produced when biomass is burned under low-oxygen conditions to release energy. This revolutionary approach may offer a long-term soil-based solution to the global climate change problem.
Collaborators: Argonne National Laboratory, Oak Ridge National Laboratory, Joint Global Change Research Institute
Funding agency: U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research
Citation: Jastrow JD, JE Amonette, and VL Bailey. 2007. "Mechanisms controlling soil carbon turnover and their potential application for enhancing carbon sequestration." Climatic Change 80(1-2):5-23.