Low-level nitrogen deposition significantly inhibits methane uptake from an alpine meadow soil on the Qinghai-Tibetan Plateau

It is crucial to understand the effects of enhanced nitrogen (N) deposition on soil methane (CH4) uptake to develop a better comprehension of carbon (C) dynamics in terrestrial ecosystems. A two-year field study was conducted to assess the effects of various forms of N (NH4+ and N-3(-)) and associated N deposition rates (0, 10,20 and 40 kg N ha(-1) yr(-1)) on alpine meadow soil CH4 fluxes on the Qinghai-Tibetan Plateau, China. Soil CH4 fluxes, soil temperature, and soil moisture were monitored weekly using the static chamber technique and gas chromatography. Soil inorganic N pools, soil pH and aboveground biomass were measured monthly to examine the key controlling factors of soil CH4 flux. Our results showed that N addition significantly promoted plant growth and changed soil water-filled pore space (WFPS), but did not alter soil inorganic N storages over the short term. Low rates of N addition significantly decreased the seasonal amount of CH4 uptake by 8.6% compared with the control. Soil CH4 fluxes were mainly determined by soil WFPS, followed by inorganic N availability. N addition increased the contribution of soil WFPS, pH and soil NO3- storage. The observed reduction in CH4 uptake caused by N addition may be largely due to a decrease in physical diffusion, as the biochemical inhibition effects on methanotrophic bacteria are minor. These results suggest that soil inorganic N is a regulatory factor of soil CH4 uptake, and its promotion or inhibition to soil CH4 uptake depends on the N status in terrestrial ecosystems. (C) 2013 Elsevier B.V. All rights reserved.