Diurnal Variation in Methane Flux and Ecosystem Respiration Rate During the Growing Season in Hulunbuir Grassland, Inner Mongolia

Using a static opaque chamber method, a field experiment was conducted in-situ in the Hulunbuir meadow grassland, Inner Mongolia, during the seeding period (2011 and 2012) and flowering period (2012) to investigate the effects of grazing and mowing on the diurnal variation in methane flux and ecosystem respiration rate. The results show that the Hulunbuir meadow grassland soils were a sink of CH₄, with the average CH₄ diurnal fluxes ranging from -23.98±6.40 to -95.96±28.57 μgCm^-2 h^-1 in the three experimental periods. The relationship between the diurnal variation in CH₄ flux and temperature is complex in the study area, and some differences were observed in the diurnal variation of soil-plant system respiratory CO₂ emission fluxes during the experimental periods. During the seeding period in 2011, the daily mean soil-plant system respiration CO₂ emission fluxes were higher than in 2012, as a result of the interaction of water and temperature. The influence of grazing on the diurnal variation of CH₄ fluxes was very limited, however, the observations suggest that grazing could have increased the daily average CH₄ flux from 12.05% to 93.35% during the seeding period in 2011 and the flowering period in 2012, but reduced it from 23.32% to 30.43% during the seeding period in 2012. Mowing could be responsible for a decrease in the average daily CH₄ flux, from 11.55% to 60.62%. Considering the cumulative daily carbon emissions, CH₄ absorption accounts for only 0.35%-2.62% of the total in the Hulunbuir meadow grasslands. Moreover, the impact of grazing and mowing on the mean cumulative daily carbon emissions differed significantly between the different phenological periods and vegetation types.