Effects of irrigation on CO2 and CH4 fluxes from Mongolian steppe soil

Semi-arid temperate steppes comprise approximately 30% of the world's temperate grassland, and consequently, are a significant component of the global carbon cycle. To better understand how precipitation affects soil carbon fluxes in semi-arid steppes, we examined the effects of irrigation (simulated rainfall) on CO2 and CH4 fluxes from Mongolian semi-arid steppe soil on 10-12 August 2002 and 19-22 August 2003. Meteorological data revealed that the soil was dry in 2002 and wet in 2003. Summer flux measurements in both years showed that the soil emitted CO2 at 75-250 mg m(-7) h(-1) and consumed atmospheric CH4 at 30-90 mu g m(-2) h(-1). In 2002, the CO2 flux of the irrigated soil showed an increase of 50% over one day following irrigation compared to the non-irrigated soil, and thereafter, no increase. This enhancing effect of irrigation was found only immediately following irrigation in 2003. Soil CH4 fluxes showed little difference between the irrigated and non-irrigated soils in 2002 and 2003. There was also little difference in soil temperatures (at the surface and 5 cm depth) between the soils in 2002 and 2003. The water content of the irrigated soil increased following irrigation then rapidly decreased with time. These results demonstrate that rainfall events enhance carbon loss from semi-arid steppe soil at least within the day following irrigation. However, long-term meteorological observations of precipitation and soil water content in 2003 and 2004 suggest that usual rainfall pulses throughout the growing season (June-September) do not markedly enhance CO2 emission from such soils. (c) 2006 Elsevier B.V. All rights reserved.