Response of soil methane uptake to simulated nitrogen deposition and grazing management across three types of steppe in Inner Mongolia, China.

The response of soil methane (CH) uptake to increased nitrogen (N) deposition and grazing management was studied in three types of steppe (i.e., meadow steppe, typical steppe, and desert steppe) in Inner Mongolia, China. The experiment was designed with four simulated N deposition rates such as 0, 50, 100, and 200kgNha, respectively, under grazed and fenced management treatments. Results showed that the investigated steppes were significant sinks for CH, with an uptake flux of 1.12-3.36kgha over the grass growing season and that the magnitude of CH uptake significantly (P<0.05) decreased with increasing N deposition rates. The soil CH uptake rates were highest in the desert steppe, moderate in the typical steppe, and lowest in the meadow steppe. Compared with grazed plots, fencing increased the CH uptake by 4.7-40.2% with a mean value of 20.2% across the three different steppe types. The responses of soil CH uptake to N deposition in the continental steppe varied depending on the N deposition rate, steppe type, and grazing management. A significantly positive correlation between CH uptake and soil temperature was found in this study, whereas no significant relationship between soil moisture and CH uptake occurred. Our results may contribute to the improvement of model parameterization for simulating biosphere-atmosphere CH exchange processes and for evaluating the climate change feedback on CH soil uptake.