## 4 Discussion
### Influencing Factors of CUE and WUE Variation in the NMR  
The vegetation CUE of NMR tended to have an inverse relationship with precipitation (80.65%), with the majority of areas showing a non-significant negative correlation. This result aligns with findings from previous studies in South China, where vegetation CUE showed a weak inverse relationship to precipitation that was not statistically significant [17]. Regions showing a notable inverse relationship linking CUE to precipitation (5.03%) are situated in the southern and northeastern sections of the NMR, especially around Hezhou, Ganzhou, and Shaoguan. This may be due to frequent precipitation, which is often accompanied by cloudy weather, reducing sunlight and consequently affecting photosynthetic efficiency, thereby lowering CUE [55]. Furthermore, excessive precipitation may lead to soil moisture saturation, disrupting root respiration and soil microbial activity, which further diminishes CUE [56]. Conversely, areas (0.06%) showing a strong direct relationship linking CUE to precipitation are scattered, suggesting that moderate rainfall in these areas can enhance photosynthesis and favor the accumulation of organic carbon in shallow plant roots, ultimately increasing CUE [57]. Vegetation CUE also exhibits a primary negative correlation with temperature (79.56%), aligning with the findings of earlier research [17]. Temperature changes affect plant respiration rates, and a moderate increase in temperature leads to higher organic matter consumption through respiration, reducing carbon sequestration [58]. Conversely, overly elevated temperatures may hinder the photosynthetic process and suppress plant growth, further decreasing carbon fixation [59]. Regions exhibiting a notable inverse relationship linking CUE to temperature (18.09%) are predominantly situated in the southeastern section of the NMR, particularly in Hezhou, Shaoguan, Qingyuan, Heyuan, and Meizhou. These regions, compared to others, have higher population densities, greater urbanization, and more pronounced temperature fluctuations, which could account for the marked inverse relationship observed between vegetation CUE and temperature in these areas. Vegetation WUE is predominantly negatively correlated with precipitation (90.57%), aligning with the results reported by [PERSON] et al [48]. Increased temperatures lead to higher evapotranspiration rates and greater water loss, thus reducing vegetation water use efficiency [60]. Similarly, vegetation WUE exhibits an overall negative correlation with temperature (54.92%), but the proportion of positive correlation (45.08%) is not much smaller than the negative correlation. Regions exhibiting a strong direct relationship linking WUE to temperature (10.39%) are primarily concentrated in Chenzhou and Ganzhou. On one hand, favorable temperature conditions may enhance photosynthesis, while sufficient precipitation ensures that plants can effectively use water even under higher temperatures [61]. On the other hand, the temperature increase in these areas may be linked to longer growing seasons and enhanced photosynthetic activity, contributing to the observed direct relationship linking WUE to temperature [62]. The findings highlighted the complex and region-specific interactions between vegetation efficiency metrics (CUE and WUE) and climatic variables. Future research should focus on incorporating additional factors, such as soil nutrient availability, land use changes, and atmospheric CO\({}_{2}\) concentrations, to better understand their combined effects on vegetation CUE and WUE. Additionally, the role of climate extremes, such as droughts and heatwaves, deserves further exploration to predict ecosystem responses under future climate scenarios. The differing responses of vegetation types to precipitation and temperature highlight the complexity of ecosystem processes in the NMR. grasslands are the vegetation types that show the strongest inverse relationship linking CUE to precipitation, while the weakest is shrubland.