Nitrogen addition impacts on the emissions of greenhouse gases depending on the forest type : a case study in Changbai Mountain, Northeast China

Purpose Anthropogenic-induced greenhouse gas (GHG) emission rates derived from the soil are influenced by long-term nitrogen (N) deposition and N fertilization. However, our understanding of the interplay between increased N load and GHG emissions among soil aggregates is incomplete. Materials and methods Here, we conducted an incubation experiment to explore the effects of soil aggregate size and N addition on GHG emissions. The soil aggregate samples (0-10 cm) were collected from two 6-year N addition experiment sites with different vegetation types (mixed Korean pine forest vs. broad-leaved forest) in Northeast China. Carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) production were quantified from the soil samples in the laboratory using gas chromatography with 24-h intervals during the incubation (at 20 degrees C for 168 h with 80 % field water capacity). Results and discussion The results showed that the GHG emission/uptake rates were significantly higher in the micro-aggregates than in the macro-aggregates due to the higher concentration of soil bio-chemical properties (DOC, MBC, NO3-, NH4+, SOC and TN) in smaller aggregates. For the N addition treatments, the emission/uptake rates of GHG decreased after N addition across aggregate sizes especially in mixed Korean pine forest where CO2 emission was decreased about 30 %. Similar patterns in GHG emission/uptake rates expressed by per soil organic matter basis were observed in response to N addition treatments, indicating that N addition might decrease the decomposability of SOM in mixed Korean pine forest. The global warming potential (GWP) which was mainly contributed by CO2 emission (>98 %) decreased in mixed Korean pine forest after N addition but no changes in broad-leaved forest. Conclusions These findings suggest that soil aggregate size is an important factor controlling GHG emissions through mediating the content of substrate resources in temperate forest ecosystems. The inhibitory effect of N addition on the GHG emission/uptake rates depends on the forest type.