SELECTIVE PRESERVATION OF STRUCTURAL CARBOHYDRATES DURING PEAT FORMATION

The structural carbohydrate “sphagnan” has been hypothesized to play a role in slowing the degradation of Sphagnum moss, and therefore contribute to carbon sequestration in peatlands. Sphagnan is composed of a galacturonic acid and rhamnose backbone. However, it is currently unclear whether sphagnan persists beyond early-litter degradation and plays a role in the long-term preservation of organic matter in peatlands. In this study, we analyzed hydrolyzable neutral sugars, using rhamnose as a proxy for sphagnan content, and tracked the concentration of rhamnose present within moss before and after a 270-day period of decomposition, as well as the concentration of rhamnose at different depths within five peat cores collected from a southwest Michigan bog. While there was a clear increase in the relative abundance of rhamnose during the moss decomposition process, there was little change in the rhamnose concentrations within the peat cores in relation to depth. This implies that the degradation of sphagnan occurs at roughly the same rate as other sugars. However, an increase in the concentration of glucose with depth, with decreasing abundances of xylose and arabinose, indicates that cellulose is selectively preserved compared to hemicelluloses, accumulating over degradation. Overall, our results show that sphagnan is selectively preserved during litter decomposition, but other structural carbohydrates may play a larger role in the long-term preservation of organic matter in peatlands.