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 N20 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 gg C.m 2.hl） as compared to M3 （70.5 gg C .m-2.h-1） （p 〈 0.01）, and significantly higher mean N2O efftux at UM （6.3 gg N. m2. hI） as compared to M3 （4.3μg N.m2.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 moisre 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.

Pollen-inferred vegetation and environmental changes in the central Tibetan Plateau since 8200 yr BP

The ecotone between alpine steppe and meadow in the central Tibetan Plateau is sensitive to climate changes. Here we used the pollen records from three lakes in this region to reconstruct the evolution of local vegetation and climate since 8200 cal. yr BP. The history of temperature and precipitation was reconstructed quantitatively with multi-bioclimatic indexes and a transfer function from pollen records. Results show that the steppe/meadow dominated during the period of 8200―6500 cal. yr BP, especially 8200―7200 cal. yr BP, indicating the central Tibetan Plateau was controlled by strong monsoon. The steppe dominated during the periods of 6000―4900, 4400―3900, and 2800―2400 cal. yr BP. The steppe decreased gradually and the meadow expanded during the period of 4900―4400 cal. yr BP. Three century-scale drought events occurred during 5800―4900, 4400―3900 and 2800 cal. yr BP, respectively. The first time when the regional climate shifted to the present level was at 6500 cal. yr BP in the central Plateau. Since 3000 cal. yr BP, the temperature and precipitation have decreased gradually to the present level. However, the cold climate between 700―300 cal. yr BP likely corresponds to the Little Ice Age.