## 4 Discussion  
[PERSON] and [PERSON] et al. indicate that shading treatment will increase the SPAD and LAI values of rice [49; 50], which is consistent with the experimental results (CK compared with T1 and T2) presented in this paper. In summary, the shading treatment caused a decline in rice canopy spectral reflectance in the visible region and an increase in the near-infrared region. It also increased red-edge parameter values of \(\lambda_{0}\), \(D\lambda\), and \(\alpha_{0}\). However, the treatment reduced the values of A1, A2, A4, D2, A5, and D3. For the comparison of T1 and T2, when the diffuse radiation fraction improved, the SPAD and LAI values of rice increased significantly, and the rice canopy spectral reflectance also decreased in the visible region and increased in the near-infrared region. The hyperspectral reflectance of rice canopy in different wavelengths is affected by rice chlorophyll content, LAI, cell structure, leaf structure, etc. [51]. To determine the reasons for the changes in the rice canopy spectra under the increasing diffuse radiation fraction, the correlation and \(p\)-value between the rice SPAD, LAI, and the spectral reflectance in DAH 14d, DAH 21d, and DAH 28d were calculated, as shown in Figure 6.  
Figure 6a,c show that the strongest negative correlation appeared at 355 nm (\(R=-0.79\)) in DAH 14d and 405 nm (\(-0.40\)) in DAH 28d. However, the correlation in DAH 21d did not pass the test of significance (Figure 6b). The rice SPAD was negatively correlated with the reflectance of the blue-violet light band. In other words, under the increasing diffuse radiation fraction, the increasing SPAD resulted in a stronger absorption of visible light. [PERSON] revealed that the shading treatment can lead to an increase in chlorophyll b [52], which is an important factor affecting the rice canopy spectra in the visible region [53; 54]. This is consistent with the results presented in this paper. Figure 6d-f show that the strongest positive correlation appeared at 814 nm (\(R=0.62\)) in DAH 14d, 806 nm (0.66) in DAH 21d, and 934 nm (0.35) in DAH 28d. There was a  
Figure 6: The correlation between SPAD, LAI and the spectral reflectance of T1 and T2 during 2016–2017: (**a–c**) are correlations of SPAD in DAH 14d, DAH 21d, and DAH 28d; (**d–f**) are correlations of LAI in DAH 14d, DAH 21d, and DAH 28d. The sample size for calculating [PERSON]’s correlation coefficient is 108.  
strong positive correlation between the LAI value of rice and the spectral reflectivity in the near-infrared region. Therefore, under the increasing diffuse radiation fraction, the increasing LAI in rice led to increasing reflectivity in the near-infrared region [55; 56]. In addition, the canopy spectra of T1 and T2 had the largest difference between 800 nm and 900 nm, which is affected by leaf and canopy structure [57]; that is, an increase in diffuse radiation fraction may cause changes in rice leaf and canopy structure [2]. The red-edge parameters of T1 and T2 had significant changes as the SPAD value of rice leaves changed [58; 59]. The values of \(D\lambda\) and area of T2 were greater than those of T1, with no significant difference in \(\lambda_{0}\). However, [PERSON] [60] pointed out that, without shading treatment, the red-edge parameter \(\lambda_{0}\) has a strong correlation with changes in rice SPAD, and the SPAD monitoring model based on \(\lambda_{0}\) has high accuracy, which indicates that when the diffuse radiation fraction increased, the model established with the red-edge parameters \(D\lambda\) and area could have higher accuracy. For the absorption features parameters, there was also a significant difference between T1 and T2. Under the increasing fraction of diffuse radiation, both parameters A1 and A2, which are the areas of the left and right of the first absorption band (the average wavelength was in the range of 553-788 nm. ), decreased. The change in LAI, which has an impact on the shape of the first absorption band, is the main reason for the decrease in A1 and A2 [61].