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

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. An in situ experiment was conducted to investigate the effect of long-term (13-years) increased 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. Image 1 • We studied the impacts of long-term N addition on a temperate grassland. • CH 4 uptake was significantly reduced by long-term N addition. • N 2 O emission was controlled mainly by soil ammonium N rather than soil pH. • CH 4 uptake was affected mainly by soil pH and nitrate N content. • Ecosystem respiration was impacted mainly by production of forbs. Long-term increased N addition significantly reduced CH 4 uptake and enhanced N 2 O emissions, but had no significant impact on ecosystem respiration in temperate grassland. [ABSTRACT FROM AUTHOR]