Nitrogen deposition reduces methane uptake in both the growing and non-growing season in an alpine meadow

Nitrogen (N) deposition-induced N input in alpine meadow soils may affect the soil exchange of methane (CH₄) with the atmosphere. The quantities and spatiotemporal variation in CH₄ uptake remain largely unknown for this ecosystem on a global scale. Previous studies regarding CH₄ flux have mainly focused on the growing season in alpine meadows. Thus, the impact of N deposition on the non-growing season uptake of CH₄ is unknown. In this study, we investigated the effects of N deposition on CH₄ uptake during both the growing and non-growing seasons in an alpine meadow on the central Qinghai-Tibet Plateau (QTP). The CH₄ fluxes were measured using static chambers and gas chromatography in four N deposition treatment areas (Control; N7, 7 kg N ha^-1 yr^-1; N20, 20 kg N ha^-1 yr^-1; N40, 40 kg N ha^-1 yr^-1) from May 2015 to August 2018. Our results showed that alpine meadow soils acted as CH₄ sinks throughout the year. N deposition significantly decreased CH₄ uptake fluxes (P < 0.05) and the annual mean CH₄ uptake fluxes declined at N deposition levels of 7, 20, and 40 kg N ha^-1 yr^-1 by 12.3%, 14.4%, and 20.5%, respectively, compared with that of the control. Annual CH₄ uptake was significantly correlated with total annual precipitation, mean annual air temperature, and N deposition rate. Annual cumulative CH₄ uptake in the four treatments across 3 years was 75.1 mg C m^-2, where approximately 40% of the total annual CH₄ uptake occurred during the non-growing season. Our results showed that CH₄ uptake in the non-growing season cannot be ignored when estimating annual uptake of CH₄ because of the large CH₄ uptake during the non-growing season in the alpine meadow on the QTP under N deposition conditions.