Impact of 13-years of nitrogen addition on nitrous oxide and methane fluxes and ecosystem respiration in a temperate grassland
2019
Chen, Si | Hao, Tianxiang | Goulding, K. W. T. | Misselbrook, T. (Tom) | Liu, Xuejun
Nitrogen (N) fertilizer application and atmospheric N deposition will profoundly affect greenhouse gas (GHGs) emissions, especially nitrous oxide (N₂O) and methane (CH₄) fluxes and ecosystem respiration (Rₑ, i.e. CO₂ 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 N₂O and CH₄ fluxes and Rₑ 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 (N₁₂₀) and 240 (N₂₄₀) kg N ha⁻¹ decreased from 7.12 to 4.37 and 4.18, respectively, after 13 years of N inputs. Soil CH₄ uptake was significantly reduced, but N₂O emission was enhanced significantly by N addition. However, N addition had no impact on Rₑ. Structural Equation Modeling indicated that soil NH₄⁺-N content was the dominant control of N₂O emissions, but with less effect of the decreasing pH. In contrast, CH₄ uptake was generally controlled by soil pH and NO₃⁻-N content, and Rₑ by forb biomass. The measured changes in N₂O and CH₄ fluxes and Rₑ from temperate grassland will have a profoundly impact on climate change.
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