Changes of soil organic matter along thaw transects of permafrost peat plateaus in Finnmark, Norway

Le résumé fourni par la source

The thawing of permafrost peat plateaus holds the potential for a substantial release of greenhouse gases (GHG) into the atmosphere by releasing previously frozen soil carbon – thus exacerbating climate change. The release of carbon (C) into the atmosphere is governed not only by environmental conditions, and the present microbial communities, but also by the composition and the state of the soil organic matter (SOM).Therefore, we characterize and compare the composition of SOM along thaw transects at currently degrading permafrost peat plateaus in Iškoras and Áidejávri in Finnmark, Northern Norway. Samples of SOM pools were taken along chronosequential thaw transects and were investigated using organic element analysis, FTIR spectroscopy, and biomarker analysis. Compositional differences of the SOM pools are evaluated using the traditional van Krevelen diagram, additional elemental ratios considering nitrogen (N), spectral indices based on organic functionalities, and relevant biomarkers. From the analytical results, the thermodynamical state of the SOM (C oxidation state, degree of unsaturation) is determined directly. To estimate the fractional macromolecular composition a linear mixing model is used.Preliminary results of organic elemental ratios indicate site-specific compositional changes of degrading strata along the chronosequences. Generally, the stoichiometric ratios of N to other organic elements (C, H, O) are higher in Áidejávri than in Iškoras for all strata. The intact permafrost and active layer samples in Iškoras are compositionally comparable, but the degraded analogues differ compositionally – this trend is vice versa in Áidejávri. However, the carbon oxidation state and the degree of unsaturation change notably in Iškoras, while no comparable pattern is found in Áidejávri.Visualizing the samples in the van Krevelen diagram implies macromolecular differences between the present strata, while changes before and after thaw can’t be resolved. The estimated fractional macromolecular compositions indicate the expected lignin-dominated composition on the plateaus, while amino sugars & -acids are relatively enriched in the surrounding wetlands.The site-specific compositional changes of SOM along thaw transects are suspected to be governed by the N availability, which affects the thermodynamical state and, thus, the decomposition potential of the SOM during degradation.

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