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