Chemical Composition of Soil Organic Matter from a Prairie Restoration Chronosequence Using Pyrolysis Molecular Beam Mass Spectrometry.

This study was conducted to understand the biochemical composition of soil organic matter (SOM) accruing in a chronosequence of restored prairie systems including a never-tilled remnant prairie, and in an agricultural field in Batavia, IL.  A recent study revealed that aggregate mass distribution changed dramatically in the first few years after the prairie restoration, quickly returning to the distribution of the remnant prairie. However, the C concentration in the aggregates increased linearly over the same period, never reaching the level of the remnant (O’Brien and Jastrow, 2013). In this study we are interested in the quality of the SOM that accrues with time since disturbance. We hypothesize that the SOM from agricultural site and the younger prairie sites constitute more recalcitrant C compounds than the SOM from older prairie sites. We used pyrolysis-Molecular Beam Mass Spectrometry (py-MBMS) to compare the compositional variation in SOM present in four specific aggregate fractions ((silt and clay in macroaggregates (M-silt, M-clay) and silt and clay in microaggregates occluded within macroaggregates (mM-silt, mM-clay)). The py-MBMS analysis preserves the molecular structure for mass spectrometric analysis and compound identification while providing high sample throughput. The py-MBMS data were subjected to discriminant function analysis and the preliminary results support our hypothesis that there is an increased abundance of labile C compounds with increased duration since disturbance.