Nitrogen content of forest floor Oa layers affects carbon pathways and nitrogen mineralization

As a consequence of chronically high N depositions in forest ecosystems, the C-to-N ratio of forest floors has narrowed in many forest ecosystems. This might affect the sequestration of soil C and the partitioning of C during decomposition. We investigated samples from Oa layers of 15 different forest floors under Norway spruce (Picea abies Karst. L.) with varying C-to-N ratios in respect to soil respiration, N mineralization and dissolved organic carbon (DOC) release under standardized laboratory conditions. Samples were incubated aerobically at 15 °C and water holding capacity over a period of 10 months. Soil respiration decreased significantly with decreasing C-to-N and increasing N content. The release of DOC increased with increasing C-to-N ratio, while N-mineralization was not affected by C-to-N ratio and N content. Our results support the hypothesis that low C-to-N ratios in later stages of decomposition stabilize soil organic matter and that chronically high N deposition will lead to increased accumulation of C in forest floors.