Grassland ecosystems cover a large area of the land surface and play an important role in the global carbon cycle. The objectives of this study were to examine the spatial variability of gross primary production (
GPP) and ecosystem respiration (
Reco) within a semiarid grassland ecosystem and to evaluate the environmental factors that control the spatial patterns of carbon exchanges. We determined
GPP and
Reco using transparent and opaque closed chambers at nine grassland sites in central Mongolia during the summers from 2009 through 2011. To remove effects of temporal changes in radiation and temperature,
GPP and
Reco were fitted to light- and temperature-response curves. The fitting parameters (light-saturated
GPP [
Pmax], apparent quantum yield [α], standardized
Reco at 20 °C [
R20], and the temperature sensitivity [
Q10] of
Reco) were compared among the sites. The
GPP and
Reco parameters differed significantly among the sites. Spatial patterns of
Pmax and
R20 were highly correlated with plant aboveground green biomass (
AGB) and number of plant species. The
Q10 of
Reco was significantly related to soil moisture. The light-saturated
GPP normalized to the amount of
AGB did not differ significantly among the sites, whereas the
R20 residuals of the linear biomass model were correlated with soil water content and carbon/nitrogen ratios. The results suggest that, within this semiarid grassland, spatial variations of
GPP are strongly controlled by
AGB and that variations in
Reco are associated mainly with
AGB and secondarily with soil water content and soil nutrient condition.
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