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Title: Chemical indicators of cryoturbation and microbial processing throughout an alaskan permafrost soil depth profile

Author
item ERNAKOVICH, JESSICA - Colorado State University
item WALLENSTEIN, MATTHEW - Colorado State University
item Calderon, Francisco

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2015
Publication Date: 3/27/2015
Publication URL: http://handle.nal.usda.gov/10113/62018
Citation: Ernakovich, J., Wallenstein, M., Calderon, F.J. 2015. Chemical indicators of cryoturbation and microbial processing throughout an alaskan permafrost soil depth profile. Soil Science Society of America Journal. doi:10.2136/sssaj2014.10.0420.

Interpretive Summary: Despite the potential for the vast stores of permafrost carbon to be vulnerable to decomposition under climate change, we know relatively little about the chemistry of organic matter in permafrost soils. Generally, only basic characteristics, such as soil C and N, are known about permafrost organic matter. This is the first published study to use Fourier transformed mid-infrared spectroscopy (MidIR) to investigate the functional potential of the permafrost organic matter pool. We found that permafrost soils contain compounds of mixed degradability. We use these findings to better understand the potential stability or degradability of the permafrost organic matter pool, a C pool with great potential to affect our global climate. Understanding the potential availability of these carbon compounds to decomposition will decrease the uncertainty of the role of permafrost in the global carbon cycle.

Technical Abstract: Although permafrost soils contain vast stores of carbon, we know relatively little about the chemical composition of their constituent organic matter. Soil organic matter chemistry is an important predictor of decomposition rates, especially in the initial stages of decomposition. Permafrost, organic and mineral active layer soils from Sagwon Hills, AK were analyzed for total C and N, and using Fourier transformed mid-infrared spectroscopy (MidIR). The carbon and nitrogen content of the organic active layer (OAL) was significantly higher than the mineral active layer (MAL) and permafrost soils.The top of the permafrost (0-15cm) had a higher C and N content than deeper permafrost layers (16-40cm). Principle components analysis (PCA) of the MidIR spectra showed that the OAL separates from the MAL and permafrost layers based on absorbance of the organic bands characteristic of amines and OH, aliphatics, C=C, and amide III, and also because the mineral samples have absorbance characteristic of sands and clays as expected. OAL soils contained higher amounts of the bands suggestive of chemically labile compounds, however they were all also present in the permafrost and MAL soils, but in a larger abundance in the top of the permafrost than deeper permafrost or MAL. All the soils had evidence of processed material, but the compounds were different between the OAL and the permafrost and MAL soils. Spectral data suggests that there is more labile C in the OAL than the top of the permafrost (0-15cm), which in turn has more labile C than the MAL and deeper permafrost (16+ cm). This type of detailed chemical analysis of permafrost soils will decrease the uncertainty of role of permafrost in the global carbon cycle as we increase our understanding of the availability of these carbon compounds to decomposition.