## 3 Results  
### Analysis of Inter-Monthly Temporal Variation in Corn NPP  
Using the CASA model and the mean value approach, this study simulated the corn NPP in the Fen River Basin from May to October. Subsequently, an analysis was conducted to examine temporal trends (Figure 2) and spatial distribution patterns (Figure 3).  
The analysis of temporal changes in corn NPP within the Fen River Basin, spanning May to October, revealed a distinctive single-peak pattern characterized by an initial increase followed by a decline. The average total NPP during this period was 368.65 gC/m\({}^{2}\). August exhibited the highest average NPP, reaching a peak of 131.71 gC/m\({}^{2}\), while October records the lowest average NPP at 11.53 gC/m\({}^{2}\). The descending order of average NPP values was as follows: September (74.68 gC/m\({}^{2}\)), June (63.16 gC/m\({}^{2}\)), July (45.26 gC/m\({}^{2}\)), and May (42.30 gC/m\({}^{2}\)). Examining the corn growth stages, NPP values demonstrated a gradual increase from May to June during the seedling stage, followed by a decline from June to July during the modulation stage. Subsequently, NPP experienced a rapid increase, peaking from July to August during the tasseling stage and gradually decreasing from August to September during the silking stage. Finally, NPP decreased to its minimum level from September to October, corresponding to the maturity stage.  
The spatial distribution of corn NPP in the Fen River Basin exhibited variations ranging from 0.34 gC/m\({}^{2}\) to 177.99 gC/m\({}^{2}\) during the period of May to October in 2020. Notably, the central section of the Fen River Basin displayed the highest ability for carbon capture and yielded the largest NPP compared to the upper and lower sections. Specifically, in May, corn NPP ranged from 5.24 gC/m\({}^{2}\) to 148.34 gC/m\({}^{2}\), with the lower reaches surpassing the middle section and the middle section exceeding the upper section. June witnessed corn NPP ranging from 6.88 gC/m\({}^{2}\) to 159.43 gC/m\({}^{2}\), with the middle section surpassing the lower reaches. In July, NPP ranged from 1.65 gC/m\({}^{2}\) to 84.26 gC/m\({}^{2}\), where the middle section outperformed the upper section and the upper section exceeded the lower section. August showed the peak of corn growth and NPP, with the middle section recording the highest values, followed by the upper section and then the lower section. In September, corn NPP exhibited a gradient, with higher values in the upper section, followed by the middle section, and the lowest in the lower section. The range of corn NPP in September spanned from 2.32 gC/m\({}^{2}\) to 118.11 gC/m\({}^{2}\). The autumn harvest occurred in October, representing the lowest NPP, ranging from 0.34 gC/m\({}^{2}\) to 43.11 gC/m\({}^{2}\). The upper section displayed a higher NPP than the lower section, which surpassed the middle section. Several observations can be made based on an analysis of the environment, topography, and human activities in the Fen River Basin. In the middle reaches of the Fen River, predominant land-use types included woodland, grassland, and cropland, characterized by high vegetation cover and elevated corn NPP. Conversely, the upper reaches had less cropland, which was affected by significant human activities, resulting in lower corn NPP values. In the lower reaches, the cropland area was more extensive, albeit with reduced woodland andgrassland coverage, resulting in corn NPP values falling between those observed in the middle and upper reaches.  
Figure 3: Geographical distribution characteristics of corn NPP from May to October in the Fen River Basin.  
Figure 2: Temporal trends of corn NPP from May to October in the Fen River Basin.