Different responses of CO₂, CH₄, and N₂O fluxes to seasonally asymmetric warming in an alpine grassland of Tianshan Mountains

Abstract. An experiment was conducted to investigate the effect of seasonally asymmetric warming on CO₂, CH₄, and N₂O fluxes in alpine grassland of Tianshan Mountains of Central Asia, from October 2016 to September 2019. Our results indicated that the CO₂, CH₄ and N₂O fluxes varied in the range 0.56–98.03 mg C m⁻² h⁻¹, −94.30–0.23 μg C m⁻² h⁻¹, and −1.28–10.09 μg N m⁻² h⁻¹, respectively. The CO₂ and N₂O fluxes were negatively correlated with soil temperature, but the CH₄ fluxes decreased with the increase in temperature. Furthermore, the variation in greenhouse gas flux under seasonally asymmetric warming was different between the growing season (June to September) and the non-growing season (October to May). In addition, the response rates of CO₂ and N₂O fluxes to temperature increases was significantly reduced due to warming throughout the year. Warming during the growing season led to a significant decrease in the response rate of CO₂ flux to temperature increases. However, warming during the non-growing season caused a significant increase in the response rate of CO₂ flux to temperature increases. The response rate of CH₄ flux was insensitive to temperature increase under seasonally asymmetric warming. Thus, the main finding of our results was that seasonally asymmetric warming resulted in different responses in the fluxes of individual greenhouse gases to rising temperatures in the alpine grassland.