Carbon dioxide fluxes over a temperate meadow in eastern Inner Mongolia, China

Understanding the carbon dynamics in grassland is essential to precisely estimate global atmospheric carbon budget in response to climatic change. Eddy flux measurements were carried out during 2011 and 2012 to characterize seasonal and annual variability of carbon exchanges above a temperate meadow in eastern Inner Mongolia, China. The CO2 flux showed obvious diurnal variations and the monthly mean amplitudes of diurnal course followed June/July > August > May > September. The daily maximum NEE reached up to -8.0 and -7.7 g C m(-2) for 2011 and 2012, respectively. CO2 uptake was mainly from May to August, with seasonal peaks of -16.0 g C m(-2) day(-1) in both two years. Gross primary production (GPP) and ecosystem respiration (Re) were -1,084.5, 987.1 g C m(-2) year(-1) in 2011, and -1,123.3, 1,040.2 g C m(-2) year(-1) in 2012, respectively. The meadow acted as a stable carbon sink, with integrated net ecosystem exchange (NEE) of -97.4 and -83.1 g C m(-2) year(-1) for 2011 and 2012, respectively. Compared with 2011, the ecosystem assimilated more carbon and meanwhile respired even more, leading to a less carbon sequestration in 2012. PAR and leaf area index (LAI) dominated the seasonal variations in NEE, with PAR explaining 61-69 % of the variance in NEE as LAI maintaining the plateau during June to July. Harvest significantly decreased ecosystem carbon uptake. The interannual variability in GPP and Re resulted primarily from the variations in temperature and its effect on biomass growth.