Impacts of Precipitation on Ecosystem Carbon Fluxes in Desert-Grasslands in Inner Mongolia, China

The frequency and amount of precipitation exert profound impacts on plants and the soil subsystem in dryland ecosystems. To quantitatively assess the effect of precipitation on ecosystem carbon fluxes during the growing season, a field experiment was carried out in a native desert-grassland ecosystem in Inner Mongolia to determine the dynamics of ecosystem carbon fluxes along a precipitation gradient (−60%, −40%, −20%, CK, +20%, +40%, and +60%; CK is natural precipitation). The net ecosystem productivity (NEP) and gross ecosystem productivity (GEP) exhibited a single peak, whereas ecosystem respiration (Reco) exhibited a bimodal peak across all precipitation treatments. Reco reached its highest value at the beginning of August, whereas NEP and GEP reached their highest values at the end of August. Mean values of carbon fluxes increased with an increase in precipitation (from NEP: 0.06 μmol · m ⁻²  · s ⁻¹ , Reco: 0.37 μmol · m ⁻²  · s ⁻¹ , GEP: 0.42 μmol · m ⁻²  · s ⁻¹ at −60% to NEP: 1.25 μmol · m ⁻²  · s ⁻¹ , Reco: 0.93 μmol · m ⁻²  · s ⁻¹ , and GEP: 2.18 μmol · m ⁻²  · s ⁻¹ at +60%). Increased precipitation stimulated GEP more so than Reco during the growing season, resulting in an enhanced NEP, and decreased precipitation reduced GEP more so than Reco, leading to a reduced NEP. We concluded that the carbon sequestration capacity was enhanced by increased precipitation in the desert-grassland ecosystem.