What happens when living organisms die? They decompose. The basics of the life cycle are well known to most people. In the terrestrial carbon cycle, plants use photosynthesis to harvest energy from the sun and carbon dioxide from the atmosphere, storing them as carbon-rich materials in their tissues.
When a plant dies, its remnants decompose and gradually become part of the soil, known as soil organic matter. These plant residues are the primary source of new carbon in the soil, which is either stored or used by new living things to grow and thrive. Thus, the decomposition of plant remnants is a vital pathway for transferring the sun’s energy to the terrestrial environment.
Soil scientists know much about this process, because soil organic matter is an important storehouse in the carbon cycle, which is key to the Earth’s ability to sustain life. Scientists believe that advances in understanding soil carbon could be the key to improving food security and water quality.
Recent studies have investigated erosion’s role in redistributing and burying carbon in soil. Studies conducted across Canada show that erosion-buried soil organic carbon is abundant in all kinds of agricultural landscapes and appears to be resistant to biodegradation (that is, being processed by microorganisms and returned to the atmosphere as carbon dioxide (CO2).
The carbon buried in these eroded layers is important because, so long as it remains buried, it is stable and will not return to the atmosphere. More research is needed to find out what will happen to this carbon if it becomes exposed at the surface again.
Scientists also know that microorganisms play a big role in releasing carbon and other nutrients in soil. These microorganisms can include everything from fungi to bacteria to nematodes — each plays a unique role in the nutrient cycling micro-community.
But, over time, what becomes of the microbial community associated with buried, eroded soil? How is it that much of the buried organic carbon is not simply used by the microorganisms and released as CO2 as time passes?
Sophisticated techniques for organic matter and microbial analysis are being combined to understand if and how microorganisms might control carbon stabilization in these widespread, yet unexplored erosion-buried soils.
Recent studies led by Drs. Bobbi Helgason and Bert VandenBygaart of Agriculture and Agri-Food Canada (AAFC) show that soil redistribution and burial results in carbon stores with microbial communities similar in abundance to those at the soil surface, which would seem to indicate that low oxygen and temperature at depth may play a less important role than previously thought and that it may be lack of carbon (energy) and nutrients that are most limiting for the microbes deeper in the soil profile.
"Erosion due to historical agricultural practices has buried significant stores of organic carbon in landscapes. Conservation practices have curtailed this type of soil erosion and are now rebuilding carbon in the previously eroded surface soils,” says Bobbi Helgason, research scientist, Agriculture and Agri-Food Canada.
“The presence of abundant and diverse microbial communities in the buried soils suggests that there could be potential for enhanced carbon loss under changing conditions, such as climate change or modified land use. However, our work indicates that the buried carbon is largely resistant to biodegradation."
While other factors (such as temperature and chemical composition of the soil) also play a role in the microbial community’s ability to process stored carbon and nutrients into plant-useable form, these recent studies highlight the need to find out more about how improving soil carbon management could help address global environmental challenges and increased demand for food.