Using C/N ratios to investigate DOM reactivity in northern peatlands

We investigated the difference in DOM reactivity in northern peatlands using C/N ratios of the peat, DOM, and inorganic constituents (DIC/ammonium). Previous studies have shown a difference in reactivity between the bog and fen environments using 14C. In sedge-dominated peatlands, the 14C content of the products of respiration, CH4 and DIC are essentially the same, and are similar to that of DOM. In Sphagnum-woody plant dominated peatlands with few sedges, however, the respiration products are similar but intermediate between the 14C content of the solid-phase peat and the DOM. Data indicate qualitative differences in the pore-water DOM depending on the extent of sedge cover, consistent with the hypothesis that the DOM in sedge-dominated peatlands is more reactive than DOM in peatlands where Sphagnum is dominant. C/N ratios were used to further test this hypothesis. The C/N ratios compared were the solid phase C/N for the peat, the dissolved organic carbon to the dissolved organic nitrogen for the DOM, and the dissolved inorganic carbon to the dissolved ammonium for the respiration products. We assume low C/N ratios suggest more lability of a compound. Results suggest a distinction between solid phase peat C/N ratios between the bogs and fens. Bog peat had a higher C/N ratio than fen peat with a median value of 39. Fen solid phase peat was lower with a median value of 20. These results were shown to have a statistically significant difference (P = <0.0001). Analysis of C/N ratios of the DOM between the two environments, also, yielded a difference. Overall, fen DOM had lower C/N ratios than bog DOM. The fen C/N ratio of the DOM had a median value of 45 while the bog median value was 101. The difference was statistically significant difference (P = <0.0001). This is in agreement with the 14C data which indicates fen DOM is more labile than bog DOM. The C/N ratios of the respiration products (DIC/ammonium) showed no significant difference between the two environments.