The stable carbon (C) isotope of soil CO₂ efflux (δ¹³CO_2e) is closely associated with soil C dynamics, which have a complex feedback relationship with climate. Three levels of warming (T0: ambient temperature (15.7 °C); T1: T0 + 2 °C; T2: T0 + 4 °C) were combined with three levels of increased precipitation (W0: ambient precipitation (245.2 mm); W1: W0 + 25%; W2: W0 + 50%) in order to quantify soil CO₂ flux and its δ¹³CO_2e values under nine treatment conditions (T0W0, T0W1, T0W2, T1W0, T1W1, T1W2, T2W0, T2W1, and T2W2) in desert steppe in an experimental beginning in 2015. A non-steady state chamber system relying on Keeling plots was used to estimate δ¹³CO_2e. The temperature (ST) and moisture (SM) of soil as well as soil organic carbon content (SOC) and δ¹³C values (δ¹³C_soil) were tested in order to interpret variations in soil CO₂ efflux and δ¹³CO_2e. Sampling was carried out during the growing season in 2018 and 2019. During the experiment, the ST and SM correspondingly increased due to warming and increased precipitation. CO₂ flux ranged from 37 to 1103 mg m⁻²·h⁻¹, and emissions peaked in early August in the desert steppe. Warming of 2 °C to 4 °C stimulated a 14% to 30.9% increase in soil CO₂ efflux and a 0.4‰ to 1.8‰ enrichment in δ¹³CO_2e, respectively. Increased precipitation raised soil CO₂ efflux by 14% to 19.3%, and decreased δ¹³CO_2e by 0.5‰ to 0.9‰. There was a positive correlation between soil CO₂ efflux and ST and SOC indicating that ST affected soil CO₂ efflux by changing SOC content. Although the δ¹³CO_2e was positively correlated with ST, it was negatively correlated to SM. The decline of δ¹³CO_2e with soil moisture was predominantly due to intensified and increased diffusive fractionation. The mean δ¹³CO_2e value (−20.2‰) was higher than that of the soil carbon isotope signature at 0–20 cm (δ¹³C_soil = −22.7‰). The difference between δ¹³CO_2e and δ¹³C_soil (Δ_e-s) could be used to evaluate the likelihood of substrate utilization. ¹³C enriched stable C pools were more likely to be utilized below 20 cm under warming of 2 °C in the desert steppe. Moreover, the interaction of T × W neither altered the CO₂ emitted by soil nor the δ¹³CO_2e or Δ_e-s, indicating that warming combined with precipitation may alleviate the SOC oxidation of soil enriched in ¹³C in the desert steppe.

Harvesting is a common method in grassland management. With shrub encroachment into grassland, special hydrological and physiological dynamics probably occur in the shrub-grass coexisted ecosystem after harvesting, which remains largely unclear. Therefore, this study aims to identify potential effects of harvesting on soil moisture pattern, phenology dynamics, and water utilization in a shrub encroached grassland. We monitored soil water for a year beneath the Caragana microphylla canopy and interspace grassland after harvesting. The results showed that the soil water content increased under shrubs and grass patches after harvesting, especially under later ones. The water storage in soil of 0–100 cm depth increased by 18.9 mm under grass but only 5.5 mm under shrubs. Harvesting also decreased the difference of water storage between shrubs and grass from 19.1 to 5.7 mm. More snowmelt compensation, less evapotranspiration, shorter growing season, and higher water use efficiency may jointly contribute to the water recovery of harvesting soil. This study contributes novel evidence to the ecohydrological impacts of harvesting on shrub-grass co-existed ecosystems, shows application value in controlling shrub encroachment process and provides fundamental insights for the further study on soil water dynamics of similar ecosystems worldwide.