Alteration of Soil Organic Matter Composition After 130 Years of Afforestation Assessed by Molecular Markers

Summary Afforestation reduces carbon emissions through increased soil organic matter (SOM) stocks as well as long-term carbon sequestration. However, little is known about the alterations in the composition of organic matter (OM) after afforestation, specifically on a molecular level. The analysis of plant- and microorganism-derived molecular proxies in soil allows to trace different sources of OM and its transformation once incorporated into soil. However, focusing only on one compound class may result in flawed or incomplete conclusions due to missing information offered by other compound classes. One approach to a more reliable conclusion on the SOM dynamics is the combination of multiple compound classes. The objective of this project is to identify the major source of SOM in a subalpine afforestation sequence (40–130 years) with Norway spruce (Picea abies L.) on a former pasture in Jaun, Switzerland with the combination of multiple plant- and microorganism-derived molecular proxies. Within this project we expect a decline in SOC stocks after 50 years (72.2 t ha-1) and a recovering after 130 years (116.8 t ha-1) of afforestation. Overall, we expect an increase in SOM, a decline in SOM quality and a higher fungal PLFA content in older forests.