Print PagePermafrost soils contain a large portion of the terrestrial carbon stocks, which may be vulnerable to decomposition due to climate warming. Decomposition would release carbon dioxide and methane into the atmosphere, resulting in a positive feedback with climate change. However, the accuracy of our carbon efflux predictions is constrained by our inadequate understanding of controls on decomposition in thawed permafrost. Decomposition in thawed permafrost will be a function of both soil organic matter (SOM) chemistry and the ability of microbial communities to degrade substrates that become available. Little is currently known about SOM chemistry or microbial community traits in permafrost soils.
Permafrost cores and active-layer soils were collected from Sagwon Hills, Alaska in August of 2009. Permafrost cores and the overlying active-layer organic and mineral soils were further separated into 5 cm increments and homogenized while frozen. Soils were analyzed with Fourier-transformed Mid-infrared spectroscopy (FT-IR) to quantify the relative abundance of specific constituents of the SOM in each layer. The ability of the microbial community to degrade a variety of substrates, which correspond to different components of the SOM, was analyzed using Ecolog plates (Biolog Inc) incubated at 10°C. Measurements of carbon utilization were made every 12 hours. The data was analyzed by comparing average well color development (AWCD) as well as community level kinetic growth curves for each substrate at each depth. Linking the kinetics of microbial substrate use to soil chemistry will inform our predictions of the vulnerability of carbon stored in permafrost.
Results/Conclusions
The results from the Ecolog experiment indicate that the permafrost community utilized half as many substrates as the active-layer community (p=0.0005) contributing to a greater AWCD in the active-layer [organic= 1.20+0.18; permafrost= 0.56+0.26]. A greater proportion of the activity in the active-layer is attributable to the use of carbohydrates (p=.0037), while the permafrost and active-layer communities accessed amino acid and carboxylic acid substrates equally (p=0.8633 and p=0.1119, respectively). Analysis by FT-IR indicates that the active-layer is characterized by recent additions of organic materials, such as carbohydrates and aliphatics. The permafrost soil has more features attributable to decomposed material, but still contains large amounts of labile carbon. Both active-layer and permafrost microorganisms are well adapted to the carbon substrates available, with the active-layer able to degrade observed carbohydrates. The permafrost and active-layer microbes are able to degrade amino acids and carboxylic acids, which are observed in FT-IR analysis of the SOM.
