The response of soil respiration to different N compounds addition in a saline–alkaline grassland of northern China

Abstract

AbstractThe increase in atmospheric nitrogen (N) deposition has profound effects on soil respiration (SR). However, the responses of SR to the addition of different N compounds, particularly in saline–alkaline grasslands remain unclear. A 3-year controlled field experiment was conducted to investigate the responses of SR to different N compounds (NH4NO3, (NH4)2SO4 and NH4HCO3) during the growing seasons in a saline–alkaline grassland located in the agro-pastoral ecotone of northern China. Our results demonstrated that SR showed a bimodal pattern and a significant interannual difference that was regulated by air or soil temperature and precipitation. Nitrogen addition had a significant effect on SR, and the effect of N addition on SR varied yearly, which was related to seasonal precipitation. The mean SR across 3 years (2017–2019) was increased by 19.9%, 13.0% and 16.6% with the addition of NH4NO3, (NH4)2SO4 and NH4HCO3, respectively. The highest effect of NH4NO3 addition on SR across 3 years was ascribed to the highest aboveground net primary production, belowground net primary production (BNPP) and soil NO3− concentrations. SR (C loss) was significantly increased while plant productivity (C input) did not significantly change under NH4HCO3 addition, indicating a decrease in C sequestration. In addition, BNPP was the main direct factor influencing SR in this saline–alkaline grassland, and soil salinization (e.g. soil base cations and pH) indirectly affected SR through soil microorganisms. Notably, NH4NO3 addition overestimated the response of SR to N addition, and different N compounds should be considered, especially in saline–alkaline grassland.