Effect of mowing on N2O and CH4 fluxes emissions from the meadow-steppe grasslands of Inner Mongolia

To assess the impacts of mowing on N2O and CH4 fluxes emissions from the meadow-steppe grasslands of Inner Mongolia, China, two regimes were investigated: unmown since 2005 (UM), and mown once every three years since 2009 (M3). On-site measurements were conducted continuously during a year-round period (August 2011 to August 2012). During the observation period, three diurnal cycles were also measured. In addition, a targeted laboratory experiment was conducted to make up for the few measurements in winter. A large pulse of N2O emissions related to freeze-thaw cycles was observed at M3 during the spring thaw. Results showed that the meadow-steppes played a role as a sink for CH4 and a source for N2O. Significantly lower mean CH4 uptake at UM (40.3 mu g C center dot m(-2)center dot h(-1)) as compared to M3 (70.5 mu g C center dot m(-2)center dot h(-1)) (p < 0.01), and significantly higher mean N2O efflux at UM (6.3 mu gN center dot m(-2)center dot h(-1)) as compared to M3 (4.3 mu g N center dot m(-2)center dot h(-1)) (p < 0.05) were found. The laboratory experiment results revealed that mowing changed the soil conditions that favor the activity of denitrifiers during thawing periods. The CH4 and N2O fluxes were significantly correlated with soil temperature (p < 0.05). Mowing affected CH4 uptake and N2O emission mainly through its effect on vegetation types and some soil properties, such as soil inorganic N content, soil temperature, and soil moisture content, while soil inorganic N and moisture were not leading factors. Our results also suggested that mowing could mitigate the potential global warming in terms of CH4 uptake and N2O emissions.