Effects of long-term polymorphic nitrogen addition on soil N₂O emission in temperate artificial Quercus liaotungensis forests

  Objective  Exploring the effects of long-term nitrogen deposition on the concentration of available nitrogen and soil N₂O emissions in forest soil is important for controlling soil greenhouse gas emissions and improving the accuracy of regional carbon source sink assessment.

  Method  The effect of N addition at different levels (control, 50 kg/(ha·year), 150 kg/(ha·year)) and forms (nitrate N: NaNO₃; ammonium N: (NH₄)₂SO₄ and mixed N: NH₄NO₃) on N₂O emission from temperate plantation soils was analyzed by a field N addition control experiment using static chamber/gas chromatography.

  Result  (1) The forms and levels of N addition caused significant accumulation of soil NH₄⁺-N and NO₃⁻-N. The accumulation effect of NO₃⁻-N was much higher than that of NH₄⁺-N. (2) Soil N₂O emissions were promoted by different forms and levels of N additions. Low and high levels of NaNO₃, (NH₄)₂SO₄, and NH₄NO₃ additions increased annual cumulative soil N₂O emissions by 87.39% and 146.79%, 86.13% and 74.91%, 98.67% and 50.50%, respectively. (3) Combined with the results of our previous study, we speculated that nitrification reaction was the dominant process of N₂O emission from temperate plantation soils, and NH₄⁺-N was more efficiently converted to N₂O than NO₃⁻-N.

  Conclusion  The effect of long-term nitrogen addition on soil N₂O emissions is stage-specific. Therefore, we emphasize the importance of long-term field monitoring, and the contribution effect of N addition on soil N₂O emissions from temperate forests may be overestimated if the experimental period is short.