Spatial variability of photosynthetic production and ecosystem respiration on a hundred-kilometer scale within a Mongolian semiarid grassland

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Abstract

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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