EFFECTS OF NITROGEN ADDITION ON CARBON MINERALIZATION IN BOREAL PEATLANDS SOIL IN NORTHEAST CHINA: A LABORATORY STUDY

The increased nitrogen (N) availability caused by climate warming and associated permafrost thawing would affect the carbon (C) sequestration in high latitude ecosystems, especially in boreal peatlands. However, the effect of N availability on C mineralization of soil, especially at depths, was not sufficiently understood. In this study, we collected boreal peatland soils at different depths in Northeast China and investigated soil organic C (SOC) mineralization with three N addition levels (control: 0 mg N.g(-1) soil; low N: 0.04 mg N.g(-1)soil; high N: 0.08 mg N.g(-1)soil) in a short laboratory experiment. The results showed that after 66d incubation the total SOC mineralization as well as the percentage of initial SOC mineralization mainly decreased at depth and they were evidently correlated with initial water content, pH, and total phosphorus (P) content. N addition suppressed SOC mineralization in subsurface (30-100 cm) soil layers, and the suppression was significant at 70-80 cm and 90-100 cm depths. N addition tended to enhanced SOC mineralization in surface (0-30 cm) soil layers, and the stimulation effect was significant at 20-30 cm depth. In conclusion, our results suggested that N addition did not affect SOC mineralization significantly at 0-100 cm depths; some initial soil characteristics were the major factors that control SOC mineralization at depth.