## 4 Discussion
### The Spatiotemporal Characteristics of the Impact of Environmental Factors on GPP in Arid Regions  
Based on a comprehensive analysis of environmental factor station data from three different types of ecosystems (farmland, desert vegetation, and grassland), it is shown that PAR, Tsoil, Tair, and VPD in various ecosystems in arid areas exhibit significant seasonal variation characteristics. Higher values are observed from March to October than from November to February, with the peaks occurring in mid-summer. Desert vegetation areas have the strongest annual average attribute characteristics of environmental factors among all ecosystems, while SWC shows no significant seasonal variation. Spatially, the Gurbantunggut Desert in the Junggar Basin has the most significant spatial attribute values for the peak values of PAR, Tsoil, Tair, and VPD. In contrast, the spatial attribute values in the middle of the TM and the northernmost Altai Mountains are generally low. The spatial patterns of SWC are the opposite to those of PAR, VPD, Tair, and Tsoil. This stability in environmental factor attributes and spatial characteristics in arid regions is attributed to the perennially hot, dry, and low-rainfall conditions, particularly in desert vegetation areas where vegetation cover is relatively low [2; 65; 27]. [PERSON] et al. [66] found that the physical processes that affect GPP are complex, but the leaf area index is the most important driving factor. The leaf area index in the study area dictates the canopy structure of vegetation. This canopy structure serves as a crucial intermediate variable in how GPP responds to various environmental factors such as PAR, VPD, Tair, etc. Different environmental factors indirectly affect GPP by altering the canopy structure of vegetation, and the degree of change varies with changes in the leaf area index. This conclusion is aligned with the physical processes of factors affecting GPP in arid regions. For example, the response pattern of environmental factors to GPP in desert vegetation areas is more complex than in farmland areas (Figure 6). However, as the research area becomes warmer and wetter [67], this physical process may produce some differences in the future. A comprehensive analysis of the characteristics of the mutual influence between GPP and environmental factors under different weather conditions in arid regions shows that GPP exhibits a strong spatial correlation with the five environmental factors in different ecosystems and weather conditions. In grassland areas, regardless of whether it is sunny, cloudy, or overcast, PAR is the dominant influencing factor on GPP and SWC has the least impact. This is because the vegetation in grassland areas is relatively strong and the environmental factor characteristics are basically stable. This finding is consistent with [PERSON] et al. 's [65] study on carbon flux influencing factors in the central TM. In desert vegetation areas, PAR is the dominant influencing factor on GPP on sunny days, VPD is the dominant influencing factor on GPP on cloudy days, and Tair is the dominant influencing factor on GPP on overcast days. This is because the vegetation coverage in desert vegetation areas is low and sensitive to the comprehensive fluctuations of environmental factors. This conclusion aligns with [PERSON] et al. 's [62] study on the influencing factors of NEE in the Gurbantunggput Desert. In farmland areas, due to the comprehensive influence of human activities, PAR, VPD, Tair, and Tosil are jointly the dominant influencing factors on GPP under three weather conditions. This conclusion is broadly consistent with [PERSON] et al. 's [68] study on carbon flux influencing factors in the northwest maize drip irrigation area, and with [PERSON] et al. 's [69] exploration of the spatial-temporal changes and impact mechanisms of carbon flux in various ecosystems in semi-arid Asia.