Molecular Profiling of Permafrost Soil Organic Matter Composition and Degradation Under Warming Climate.

Molecular profiling of permafrost soil organic matter composition and degradation
under warming climate

Baohua Gu^1*, Benjamin F. Mann¹_, Evan Portier¹, Elizabeth M. Herndon¹, David Graham³, Stan Wullschleger¹_, Liyuan Liang¹.  Oak Ridge National Laboratory, Oak Ridge, TN 37831

Nikola Tolic², Stephen J. Callister², Rosalie K. Chu², Errol W. Robinson². Pacific Northwest National Laboratory, Richland, WA  99352

* Email: gub1@ornl.gov

ABSTRACT

Permafrost soil accounts for about 50% of the global belowground organic carbon (C). Rising temperatures associated with climate change are expected to increase the availability of this C source for microbial degradation and thus lead to increased production of greenhouse gases.  This study reports the application of high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) to profile molecular components of soil organic matter (SOM) and its dynamic changes during a simulated warming experiment. The soil was obtained from Barrow Environmental Observatory, Alaska, and subjected to anaerobic warming for a period of 40 days.  SOM was extracted with neutral and alkaline pH water (0.01 M KCl and 0.1 M KOH) and analyzed before and after the incubation to determine the components of the organic C that had been degraded over the course of the study. A CHO index based on molecular composition was utilized to codify SOM components according to their observed degradation potential. The carbohydrate component in the water-soluble fraction (WSF) reveals a high degradation potential, while structures with similar stoichiometries in the base-soluble fraction (BSF) are not readily degraded. The WSF of SOM shifted to a wider range of molecular masses including an increased prevalence of larger molecules, while the size distribution in the BSF changed little over the same period. An incorporation of ordered organic nitrogen in SOM was also observed in the BSF, possibly as primary and secondary amines or N-heterocycles. We suggest that molecular data represented with the CHO index may be incorporated into the global C cycling model to better predict the impact of climate warming on carbon cycling.

Presented at the symposium on “Climate change impacts on soils: Understanding and evaluating the extent and rates of reactions, processes, interactions and feedbacks controlling C and elemental cycling in soil systems and interfaces, from molecular to field, regional and global scales.” 2014 ASA/SSSA/CSSA International Annual Meetings, November 2-5, 2014, Long Beach, CA.