Title：Grazing weakens N-addition effects on soil greenhouse gas emissions in a semi-arid grassland

Authors：Zhen Wang, Xiumin Zhang, Mengyuan Wang, Lan Li, An Hu, Xianjiang Chen, Shenghua Chang, Fujiang Hou

Journal: Agricultural and Forest Meteorology

Impact factor: 6.424

Abstract: Grazing and anthropogenic nitrogen (N) enrichment co-occur in most grassland ecosystems and may have substantial effects on production of soil greenhouse gases (GHGs). Although the individual effects of N addition and grazing on soil GHGs are well understood, their long-term interactive effects on grassland soil GHGs remain unclear. We conducted seven-year in situ measurement of three major GHGs in a long-term experiment comprising grazing (no, light, moderate, and heavy grazing intensity) and N-addition treatments (control, N addition: 10 g N m^-2 year^-1) in a semi-arid grassland, to determine the effects of N addition and grazing on GHGs. We found that moderate grazing reduced cumulative CO₂ emissions by 10%?11% compared with no, light, and heavy grazing. Unusually, CH₄ emissions from soils and N₂O uptake were found in this semi-arid grassland. Soil CH₄ uptake was markedly inhibited by moderate and heavy grazing. Relative to no grazing, grazing significantly reduced 60%?88% N₂O uptake over seven years on average. Nitrogen addition alone increased cumulative CO₂ emissions by 16% relative to control. An antagonistic effect between grazing and N addition was found on cumulative CO₂ emissions, cumulative CH₄ uptake, and global warming potential (GWP). Light grazing on this semi-arid grassland could offset 14% of the soil GHG emissions induced by N addition. Soil NO₃^--N was the most important factor controlling soil CO₂ emissions and CH₄ uptake, and soil pH was a major factor mediating soil N₂O uptake or consumption. Our study highlights the importance that adjusting the grazing intensity of grassland is one of efficient strategies to mitigate GHGs emissions in the context of climate change.

Linkage: https://doi.org/10.1016/j.agrformet.2023.109423

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