## 4 Discussion
### Correlation between Climate Factors and ANPP  
Temperature and precipitation have always been the two most commonly used factors in studying the driving models between ANPP and meteorological elements [49; 64; 76; 96; 97; 98; 99], as they largely affect the growth and distribution of vegetation. However, previous studies have not reached consistent conclusions regarding the impact of these two meteorological factors on ANPP. Studies reporting both positive and adverse effects of these factors on ANPP have been documented [48; 62; 65; 96]. This study largely agrees with the conclusion that temperature has a positive effect on ANPP, with 65.14% of the regions showing a positive correlation between temperature and ANPP, and a trend of temperature increase was observed in areas with positive correlations. Therefore, in these regions, the increase in temperature leading to a rise in ANPP might be due to the fact that, under the global warming trends in the study area, a temperature increase before reaching the optimum growth temperature can enhance soil microbial activity, improve photosynthetic efficiency, and promote organic matter accumulation in plants [97; 98], thereby improving productivity. Another possible reason is that the rise in temperature advances the phenological phase of the vegetation, extending the growth period and accelerating the photosynthesis process, which promotes the carbon assimilation process and biomass accumulation [100]. However, in areas within the research region where the temperature was negatively correlated with ANPP, these were mainly distributed in the central and northern parts of Yunnan Province, the central high altitude areas of Taiwan Province, and the central and southern parts of Hubei Province. We observed a trend of temperature increase in the middle and upper areas of Yunnan Province and the central high-elevation areas of Taiwan Province, implying that in these areas, the rise in temperature has a negative effect on ANPP, leading to a decrease in ANPP. This might be because global warming increases the evapotranspiration of the ecosystem, which intensifies soil water shortage, restricting vegetation growth and reducing ANPP [76; 99]. Another part of the reason could be that in high altitude areas, global warming causes snow and ice to melt, increasing soil moisture at plant root zones, causing plants to be in an anaerobic state, which in turn leads to a decrease in ANPP [101]. In the southern part of Hubei Province, we observed a trend of temperature decrease, which in this area promotes vegetation growth, resulting in an increase in ANPP. The Han River Plain, located in the heart of Hubei Province and extending southwards, encompasses a vast expanse of farmland and stands as one of the key grain-producing bases. Studies have shown that the arable land area in the Han River Plain is gradually expanding [67; 68], and with the continuous upgrading of agricultural technology, its yield is expected to increase. The rapid increase in crop yield is likely the primary reason for the increase in ANPP in this area, and its impact outweighs the negative effects of a temperature decrease on ANPP, possibly being the reason why the ANPP increased in this region despite the downward trend in temperature. Changes in precipitation can influence the growth of plant root systems and the supply of moisture [102]. In our study, precipitation was found to be a more significant enhancer of ANPP, as approximately 60% of the regions exhibited a positive correlation between precipitation and ANPP. These areas have experienced a yearly rise in precipitation, suggesting that the increase in rainfall positively influences vegetation growth in these regions. Precipitation represents the maximum amount of water available to regional vegetation [51]. The level of precipitation directly affects the soil moisture content, which is a key factor linking precipitation and ANPP.