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

Abstract

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.