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A randomised block experiment was conducted to study the response of plant community characteristics (biomass, density and diversity) and ecosystem carbon exchange processes to warming, increased precipitation and their combination on Stipa steppe in Inner Mongolia. Increased precipitation enhanced the effect that warming had in promoting community diversity and biomass. Increased precipitation directly increased net ecosystem exchange and gross ecosystem productivity, although ecosystem respiration and soil respiration also increased. However, warming did not have a significant effect on net ecosystem exchange and gross ecosystem productivity, whereas ecosystem respiration and soil respiration were significantly decreased by warming. All carbon flux processes had a significantly positive correlation with soil moisture. However, the carbon sequestration processes, gross ecosystem productivity and net ecosystem exchange, were significantly negatively correlated with temperature, contrary to carbon emission processes, soil respiration and ecosystem respiration. Results suggest that Stipa steppe may be benefited by future climate change, as the predicted precipitation is increasing with warming in Inner Mongolia. However, it is hard to predict the feedback of Stipa steppe to climate, because of the uncertainty in magnitude and temporal dynamics of climate change. To reveal the mechanism of the observed responses, further studies are suggested in this region on the effects of altered climate variables on plant species interactions, soil organic carbon composition, soil extracellular enzyme activity, microbial biomass and microbial respiration.

Aspects of carbon exchange were investigated in typical steppe east of Xilinhot city in Inner Mongolia. Four treatments with four replicates were imposed in a randomised block design: Control (C), warming (T), increased precipitation (P) and combined warming and increased precipitation (TP). Increased precipitation significantly increased both ecosystem respiration (ER) and soil respiration (SR) rates. Warming significantly reduced the ER rate but not the SR rate. The combination of increased precipitation and warming produced an intermediate response. The sensitivity of ER and SR to soil temperature and air temperature was assessed by calculating Q10 values: the increase in respiration for a 10°C increase in temperature. Q10 was lowest under T and TP, and highest under P. Both ER and SR all had significantly positive correlation with soil moisture. Increased precipitation increased net ecosystem exchange and gross ecosystem productivity, whereas warming reduced them. The combination of warming and increased precipitation had an intermediate effect. Both net ecosystem exchange and gross ecosystem productivity were positively related to soil moisture and negatively related to soil and air temperature. These findings suggest that predicted climate change in this region, involving both increased precipitation and warmer temperatures, will increase the net ecosystem exchange in the Stipa steppe meaning that the ecosystem will fix more carbon.

The responses of plant community diversity and sward characteristics to temperature and moisture changes on the Stipa steppe in Inner Mongolia were investigated in the growing season from 2013 to 2015. Warming significantly (P<0.05) increased biomass and density. Highest biomass and density were achieved with warming and precipitation combined, whereas increased precipitation alone had no significant effect. Warming increased the Shannon–Weiner diversity index, which was significantly correlated with both air temperature (R2=0.45, P<0.05) and soil temperature (R2=0.255 P<0.05), and it was further increased by the combination of warming and increased precipitation. The Simpson index, an alternative measure of diversity that is not as sensitive to species richness, was less responsive to either warming or increased precipitation. Overall, warming had a more substantial effect than increased precipitation on the characteristics of the Stipa steppe community. However, its impact was complex, with significant variance among the 3 years of the study. The impacts of future changes in precipitation are also likely to be complex and warrant further research.

Both temperature and precipitation are predicted to increase in the region of the Stipa steppe of Inner Mongolia. We conducted an experiment to simulate both the individual and combined effects of warming and increased precipitation on community structure (biomass and diversity) and ecological processes (soil respiration and ecosystem carbon exchange). Open-topped chambers were used to simulate climatic warming, and irrigation was applied to simulate a 20% increase in precipitation. Open-topped chambers were effective in producing significant increases in mean air temperature in each year of the experiment (2011–2015), with the average increase ranging from 2.5°C to 3°C in the final 3 years of the study. Mean soil temperature was significantly increased in 2 of the 5 years of observation. Irrigation significantly increased soil moisture. The experimental treatments thus produced environmental changes consistent with those expected in the region by mid-century and provide a basis for examining the likely effects of climate change on the grassland ecosystem as reported in companion papers.

The response of soil respiration to simulated climatic warming and increased precipitation was evaluated on the arid–semi-arid Stipa steppe of Inner Mongolia. Soil respiration rate had a single peak during the growing season, reaching a maximum in July under all treatments. Soil temperature, soil moisture and their interaction influenced the soil respiration rate. Relative to the control, warming alone reduced the soil respiration rate by 15.6±7.0%, whereas increased precipitation alone increased the soil respiration rate by 52.6±42.1%. The combination of warming and increased precipitation increased the soil respiration rate by 22.4±11.2%. When temperature was increased, soil respiration rate was more sensitive to soil moisture than to soil temperature, although the reverse applied when precipitation was increased. Under the experimental precipitation (20% above natural rainfall) applied in the experiment, soil moisture was the primary factor limiting soil respiration, but soil temperature may become limiting under higher soil moisture levels.