Impact of 13-years of nitrogen addition on nitrous oxide and methane fluxes and ecosystem respiration in a temperate grassland

Abstract Nitrogen (N) fertilizer application and atmospheric N deposition will profoundly affect greenhouse gas (GHGs) emissions, especially nitrous oxide (N 2 O) and methane (CH 4 ) fluxes and ecosystem respiration (R e , i.e. CO 2 emissions). However, the impacts of long-term N inputs and the often associated N-induced soil acidification on GHG fluxes in arid and semi-arid ecosystems, especially temperate grasslands, are still uncertain. An in situ experiment was conducted to investigate the effect of long-term (13-years) N addition on N 2 O and CH 4 fluxes and R e from a temperate grassland in Inner Mongolia, northeast China, from April 2017 to October 2018. Soil pH values in the 0–5 cm layer receiving 120 (N 120 ) and 240 (N 240 ) kg N ha −1 decreased from 7.12 to 4.37 and 4.18, respectively, after 13 years of N inputs. Soil CH 4 uptake was significantly reduced, but N 2 O emission was enhanced significantly by N addition. However, N addition had no impact on R e . Structural Equation Modeling indicated that soil NH 4 + -N content was the dominant control of N 2 O emissions, but with less effect of the decreasing pH. In contrast, CH 4 uptake was generally controlled by soil pH and NO 3 − -N content, and R e by forb biomass. The measured changes in N 2 O and CH 4 fluxes and R e from temperate grassland will have a profoundly impact on climate change.