## 3 Results
### Response of CO\({}_{2}\) Fluxes to Temperature  
#### 3.3.1 Relationship between CO\({}_{2}\) Fluxes and Temperature  
To further characterize the effect of soil temperature on CO\({}_{2}\) fluxes, we fitted the function curves of soil temperature and CO\({}_{2}\) fluxes for each stratum (Figure 9). The study showed that soil temperature and CO\({}_{2}\) fluxes at different depths exhibited a univariate  
Figure 8: Ranking of the contribution of meteorological factors affecting CO\({}_{2}\) fluxes. (**a**) On a half-hourly scale; and (**b**) on a daily scale. ** represents passing the 99% significance test; * represents passing the 95% significance test.  
linear regression, and the correlation between soil temperature and CO\({}_{2}\) fluxes improved with the increasing soil temperature. Soil temperature and NEE at different depths exhibited a negative correlation, meaning that NEE decreased as the soil temperature increased. The correlations between Ts\({}_{0\text{cm}}\), Ts\({}_{5\text{cm}}\), Ts\({}_{10\text{cm}}\), and Ts\({}_{20\text{cm}}\) with NEE are 0.04, 0.09, 0.10, and 0.11, respectively (Figure 9a-d). The correlation between soil temperature and GPP at different depths was positive, indicating that the respiration of the grassland ecosystem increased more than photosynthesis with the increase in soil temperature, leading to increased GPP. The correlations between Ts\({}_{0\text{cm}}\), Ts\({}_{5\text{cm}}\), Ts\({}_{10\text{cm}}\), and Ts\({}_{20\text{cm}}\) with GPP are 0.16, 0.25, 0.26, and 0.27, respectively (Figure 9e-h). The relationship between soil temperature at different depths and NEE and GPP was tested for significance, effectively demonstrating that soil temperature is an important indicator influencing carbon flux in the Middle Tien Shan grassland ecosystem.  
To further investigate the effect of temperature on carbon fluxes in grassland ecosystems, a curve was fitted as a function of temperature and CO\({}_{2}\) fluxes using different temperature gradients (Figure 10). From the figure, it can be observed that, similarly to the relationship between soil temperature and CO\({}_{2}\) fluxes, the temperature of different gradients showed a univariate linear regression with a negative correlation between NEE and temperature, and an exponential distribution with a positive correlation between GPP and temperature. The correlation between air temperature and CO\({}_{2}\) fluxes was significantly higher than that of soil temperature, indicating that air temperature is also an important factor in regulating CO\({}_{2}\) fluxes in grassland ecosystems. However, the contribution of air temperature to CO\({}_{2}\) fluxes was significantly lower than that of soil temperature (Figure 8).  
Figure 9: Relationship between CO\({}_{2}\) fluxes and soil temperature at different depths. (**a**) The relationship between 0 cm soil temperature and NEE, (**b**) the relationship between 0 cm soil temperature and GPP, (**c**) the relationship between 5 cm soil temperature and NEE, (**d**) the relationship between 5 cm soil temperature and GPP, (**e**) the relationship between 10 cm soil temperature and NEE, (**f**) the relationship between 10 cm soil temperature and GPP, (**g**) the relationship between 20 cm soil temperature and NEE, and (**h**) the relationship between 20 cm soil temperature and GPP.