## 4 Discussion  
### Diurnal Variation in NEE  
The NEE values during the study are represented in Figure 7. They are positive at night and negative during the day. This behavior is consistent with the results obtained by [PERSON] et al. (2014); [PERSON] et al. (2015), and [PERSON] et al. (2016). During daylight hours, the ecosystem functioned as a carbon dioxide (CO\({}_{2}\)) sink, with higher levels of absorption through photosynthesis compared with emissions through respiratory processes. However, during the nighttime, the ecosystem acted as a source of CO\({}_{2}\), primarily because of Reco (2017, 2018). In the absence of sunlight, NEE is, on average, 58 times lower than the results of [PERSON] et al. (2016) and [PERSON] et al. (2019). This decrease can be attributed to the higher levels of RHC during the same period (Figure 9d). As a result, the sensor did not perform at its optimal level. In contrast to portable analyzer technology, the EC methodology used in the aforementioned studies employed open-path NDIR gas analyzers such as the LI-7200, LI-7500, and EC-150. These are specifically designed to measure fluxes in CO\({}_{2}\), water vapor, and energy below the canopy. Therefore, their prices are excessively higher compare with a portable analyzer. In this study, the \"MHZ19B\" NDIR sensor was used, which differs in application, precision, and price. However, if optimal operating conditions are guaranteed, the sensor has a high potential for accuracy and practicality.  
Figure 8: Spearman correlation heat map (R) between NEE, Reco, and environmental variables. Light and dark colors indicate positive and negative correlations, respectively. “\(\ast\)” indicates a significant correlation at the 0.05 level (\(p\) < 0.05).  
On the other hand, total NEE during the vegetative phase (\(-25.2\) umolCO2 m\({}^{2}\) s\({}^{-1}\)) was 1.4 times lower than the minimum during the reproductive phase (\(-35\) umolCO2 m\({}^{2}\) s\({}^{-1}\)). Similarly, the maximum diurnal NEE during the reproductive stage (\(-13\) umolCO2 m\({}^{2}\) s\({}^{-1}\)) was 1.4 times higher than during the vegetative stage (\(-9.4\) umolCO2 m\({}^{2}\) s\({}^{-1}\)). This is consistent with [PERSON] et al. [21], who determined that the maximum absorption during the vegetative and maturation phase was approximately 1.5 times lower than in the reproductive phase. In the vegetative phase, CO\({}_{2}\) assimilation is limited because the plant is in the growth stage (Figure 10a,b). In the reproductive stage, complete development is observed, leading to maximum absorption. In the maturation stage, senescent leaves fall and add organic matter to the soil. Additionally, the plots are drained in preparation for the harvest phase. These two processes gradually increase CO\({}_{2}\) emissions until the crop is harvested (Figure 10c,d). This behavior is similar to the results of [PERSON] et al. [30].  
Figure 10: Rice field growth in different stages of the cycle. (**a–d**) Tillering (82 and 89 DPS), spindle stage (111 DPS), and flowering (126 DPS).  
Figure 9: Boxplot graphic: average diurnal variation in the main environmental factors. (**a**) Tc; (**b**) Ts; (**c**) Rn; and (**d**) Rftc.