## 4 Discussion  
### Responses of Soil Hydrothermal Characteristics and Carbon Emissions to Biochar Application  
The soil water content and soil temperature are important physical characteristics of soil, and they are affected by many factors such as climate, topography, and agronomic measures. Biochar has many hydrophilic functional groups, a large specific surface area,  
Figure 10: Characteristics of net ecosystem carbon budget in winter wheat fields under different amounts of added biochar in 2018–2019 and 2020–2021. Note: NPP represents net primary production, GPP represents gross primary production, and NECB represents net ecosystem carbon budget. Figure 9: Wheat yield (**A**), total gaseous carbon emissions (**B**), and carbon emission efficiency (**C**) under different amounts of added biochar in 2018–2019 and 2020–2021. Note: TCCE represents total gaseous carbon emissions and CEE represents carbon emission efficiency. Values represent means \(\pm\) standard errors and different lowercase letters indicate significant differences between treatments (Duncan’s test, \(p<0.05\)). and high porosity, which contribute to improved soil water retention [57; 58]. Studies have shown that the application of biochar can increase the soil water content in farmland [59; 60]. Similar to previous studies, the results obtained in the present study showed that the application of biochar significantly increased the soil water content in wheat fields. In addition, [PERSON] et al. [61] found that the application of biochar could increase the soil temperature, and suggested that this may have been related to the effect of biochar on promoting the absorption of solar radiation by the soil. Furthermore, [PERSON] et al. [62] showed that the application of biochar reduced the variations in the soil temperature range. Moreover, [PERSON] et al. [63] found that biochar changed the soil thermal properties by increasing the total soil porosity, which may have reduced the fluctuations in the soil temperature. Similar to previous studies, we found that the application of biochar increased the average soil temperature during the wheat growth period and reduced the fluctuations in the soil temperature. The emission of CO\({}_{2}\) from the soil is an important pathway that allows carbon to flow from the soil carbon pool to the atmospheric carbon pool, and these emissions are affected by the physical and chemical properties of soil and biological processes. Biochar can inhibit the mineralization of soil organic carbon by adsorbing soluble organic carbon and promoting the formation of agglomerations [64]. In addition, biochar can slow down the decomposition of soil carbon by inhibiting the activity of glucosidase and microbial growth [65; 66; 67]. [PERSON] et al. [68] conducted biochar application trials in irrigated farmland and showed that the application of 22.4 Mg ha\({}^{-1}\) biochar significantly reduced soil CO\({}_{2}\) emissions by 20%. Similarly, [PERSON] et al. [69] found that the application of biochar in a subtropical bamboo forest reduced cumulative CO\({}_{2}\) emissions. Similar to most previous studies, we found that the application of biochar significantly reduced cumulative CO\({}_{2}\)-C emissions by 7.51-31.07% in wheat fields. The emission (or uptake) of soil CH\({}_{4}\) is determined by CH\({}_{4}\) production and oxidation processes, which are mainly regulated by methanogenic bacteria and methane-oxidizing bacteria [70]. Biochar application can increase the abundance of methane-oxidizing bacteria and reduce the ratio of methanogenic bacteria relative to methane-oxidizing bacteria, which is conducive to the CH\({}_{4}\) oxidation process [70; 71]. [PERSON] et al. [37] showed that the application of biochar could significantly reduce CH\({}_{4}\) emissions from rice fields. Similarly, [PERSON] et al. [72] demonstrated that the application of 9 Mg ha\({}^{-1}\) biochar increased the CH\({}_{4}\) uptake amount by 96%. Furthermore, [PERSON] et al.