Earth Sciences Division (ESD) Department of Energy (DOE) Lawrence Berkeley National Laboratory (LBNL)

Ecology Department Core Capability - Carbon Cycling & Climate Change Ecology (CCE)

Permafrost represents one of the Earth’s largest carbon reservoirs, holding an estimated 960 gigatons (Gt) of carbon. Widespread thawing of previously frozen soils is predicted under global warming scenarios, allowing microbial decomposition of organic matter and resulting in release large quantities of carbon dioxide and methane into the atmosphere. The amount of carbon dioxide released by permafrost depends on the speed and extent of thawing, but research indicates that it could reach up to one Gt per year if current warming trends continue. In most locations, the top layer of soil, called the active layer, thaws annually allowing plants to grow and microbes to decompose defrosted organic material. Global warming threatens to deepen the active layer or thaw the permafrost completely depending on location, soil, and vegetation types. Predicting the future of carbon and methane emissions from thawing permafrost is an extremely difficult problem but is critical in climate change models due to the vast amounts of carbon that have the potential for release into the atmosphere. Our hypothesis is that most microbes are largely inactive in permafrost but some become active at higher temperatures as the permafrost thaws, break down organic carbon that is currently sequestered, and release large amounts of carbon dioxide and methane into the atmosphere. In addition, we predict that the relative amounts of carbon dioxide and methane produced are going to be dependent on the particular members of the community that grow. For example, methanogenic archaea will be the dominant methane producers under anaerobic incubation conditions. 16S rRNA gene profiling of microbial communities has revealed a diversity of microbes in the permafrost, in some instances on par with observations in temperate soils. However, these surveys offer limited information regarding the metabolic capacity of these communities and do not differentiate between active and dormant members.