Diurnal and Seasonal Variation in Methane and Nitrous Oxide Fluxes in Meadow Steppe of Inner Mongolia

Abstract

Temperate and tropical oxic soils usually exhibit low levels of atmospheric CH 4 oxidation, which are estimated to consume about 10% of the atmospheric CH 4. It has been reported that the semi_arid grasslands represent a significant global sink for CH 4 and a source of atmospheric N 2O. However, the spatial and temporal variability of methane is usually very high which may result in the uncertainty of the ecosystem’s function in the exchange of greenhouse between ecosystem and atmosphere. In order to help define the possible range of emission of N 2O and CH 4 from temperate grassland of Inner Mongolia, diurnal variation in fluxes of methane and nitrous oxide in meadow steppe in the Xilin River basin were investigated with static_chamber and GC methods on June 1, July 2, August 3 and September 1 of 1998. Suitable sampling time was also discussed with the data of diurnal variation investigation. The native meadow steppe can act as a source of atmospheric N 2O but a sink of CH 4 in which the fluxes of the two greenhouse gases had obvious diurnal variation. ANOVA results showed that there was significant difference for the fluxes of N 2O in the four months(F=6.359, p0.004), ranging between 0.282-2.134 μg N 2O_N·m -2·h -1. These background emission rates were typically similar to those in other temperate grasslands. The diurnal mean uptake rates of methane were (-52.19±19.67), (-27.20±10.57), (-126.05±9.32) and (-16.45±1.31) μg CH 4 C·m -2·h -1 for the four months respectively, which has a trend of “high_low_high_low” from the end of May through the beginning of September. The methane uptake rates were similar to those in the Colorado short_grass steppe, averaging 31.2 μg CH 4_C·m -2·h -1, compared with varieties of temperate ecosystems. It was proved that selecting 9∶00-13∶00 as sampling time for each sampling day is suitable in Xilin River basin according to the diurnal variation measurement.