## 3 Results and Discussion
In the initial stage of parasitism, due to the shielding of parasitic plants, the sum burns the leaves of host plants less, and the spectral reflectance tends to increase. However, in the middle and late stage of parasitism, the nutrient deficiency of the host plant leaves led to the weakening of sunlight reflection in this band [51,52]. Under different parasitic conditions, the position of the yellow edge is not affected, and it is all at 570 nm (Figures 5 and 6g). With the deepening of parasitic intensity, the slope of the yellow edge (CK (\(-\)0.00143) > T1 (\(-\)0.00213) > T2 (\(-\)0.00249) >T3 (\(-\)0.00264)) and the reflectivity of the green peak (CK (0.0017), T1 (0.0028), T2 (0.0039) and T3 (0.0043)) gradually decreases (Figures 5 and 6h,d). The position of the green peak presents shifts to long wave direction (CK (519), T1(519), T2(520), T3(522)) (Figures 5 and 6e). At this time, the reflectivity of the water stress wave band (Figures 4 and 6f) decreases gradually with CK (0.5425) > T1 (0.5182) > T2 (0.4938) > T3 (0.3483). Studies have shown that the spectral reflectance of vegetation in the range of 1550-1750 nm is usually closely related to the cell structure and water content of plants, which indicate the water absorption characteristics [53]. Therefore, with the deepening of the invasion degree of _Cuscutta japonica Choisy_, the cell structure of the leaves suffers certain damage. This is basically consistent with the research results of [PERSON] et al. on pine wood nematode infecting _Pinus needles_[54]. Figure 5: The first derivative spectral curves of the _Osmanthus fragrans_ leaves. Correlation between Chlorophyll Content and Spectral Characteristic Parameters of Host Plants with Different Parasitic Degree of Cuscutta japonica Choisy  
As shown in Figure 3, CCI of the host plant (_Osmanthus fragrans_) gradually decreased with the deepening of the parasitic intensity of _Cuscutta japonica Choisy_. Previous studies generally believed that chlorophyll was an important parameter to determine the characteristics of spectral reflectance curve of plant [55]. When the vegetation is in a healthy growth state and the chlorophyll content is high, the position of the red edge moves towards the long wave direction [55,56]. However, when vegetation is stressed by external environmental, such as drought stress, high temperature stress or insert damage, the red edge position tends to the short-wave direction [57]. Pearson correlation analysis was used to analyze the correlation between spectral parameters and plant functional traits (Table 2), and the correlation analysis in Table 2 was based on all the collected sample data, including four parasitic samples. It can be seen that there was an extremely significant correlation between spectral parameters and CCI. There was a significant correlation between RES and LT. RRV, RGP, RES, RWSB and CCI were have high correlation. In order to further explore the correlation between spectral parameters and plant functional traits, according to the correlation results in Table 2, the linear correlation analysis was carried out on the indicators that achieved significant correlation (Figure 7). Figure 7 showed the correlation between different spectral parameters with CCI and LT. The results of correlation analysis between plant functional traits and spectral parameters show that they show different correlations. The reflectance of red valley has the greatest correlation with chlorophyll content (y = \(-\)65913.323x + 9.783, \(R^{2}\) = 0.6888), which indicate that red edge characteristics were very sensitive to parasitic infestation and can be used to characterize changes in  
Figure 6: Dynamic trend of spectral parameters in different parasitism period.