## 3 Results and Discussion
In the range of 350-1800 nm, the spectral reflection curves of _Osmanthus fragrans_ leaves for all treatments have four main reflection peaks and five main absorption valleys, and the positions were basically the same. The reflection peaks were located at 560 nm, 1150 nm, 1300 nm and 1650 nm, and the absorption valleys were located at 350-560 nm, 600-700 nm, 950-1050 nm, 1150-1250 nm, and 1400-1500 nm, respectively. Figure 3: Changes in leaf functional traits under different parasitic intensities. Different lowercase letters indicate significant differences in parameters at the \(p\) \(<\) 0.05 level. (**a**) Chlorophyll content index, (**b**) leaf area, (**c**) leaf dry matter content, (**d**) leaf tissue density, (**e**) specific leaf area, (**f**) leaf thickness. Chlorophyll content index of _Osmanthus fragrans_ gradually decreased with the deepening of parasitism (Figure 3). Previous studies show that chlorophyll content index can better characterize the light reflection curve of plant leaves [31; 45]. Therefore, the spectral reflectance curve of the parasitized _Osmanthus fragrans_ leaves was higher than that of the non-parasitized healthy _Osmanthus fragrans_ leaves, which may be related to the decrease of chlorophyll content index. With the deepening of parasitism, the chlorophyll content index gradually decreases, so the absorption of sunlight decreases and the reflectivity increases [46]. Studies have shown that the phenomenon of plants increasing suddenly in this waveband belongs to the typical \"red edge effect\" characteristic of plants [46]. At the same time, the spectral reflectance of the leaves of the host plant (_Osmanthus fragrans_) with different relative chlorophyll contents has a higher reflection platform in the range of 750-1400 nm, which was wavy and may be affected by the cell structure of the leaves [46; 47]. Among them, the sample with the lowest reflection coefficient was the sample with the lowest chlorophyll content index (the highest parasitic intensity). The reflectance of the sample with the highest chlorophyll content (without parasitism) was the highest at 1150 nm, which was 0.958. There was a significant valley at 1350-1800 nm, which may be closely related to light absorption by water [48; 49; 50; 51]. Dynamic Changes of Spectral Characteristic Parameters of Osmanthus fragrans in Different Parasitic Stages  
After first-order differentiation of the reflectance original spectral curve, the first-order differential reflection coefficients under different parasitic intensities were obtained (Figure 5). We calculated eight typical spectral parameters under different parasitic intensities (Figure 6), and the parameter description was shown in Table 1. After _Osmanthus fragrans_ was parasitized by _Cuscuta japonica Choisy_, there was an obvious \"blue shift\" in the red edge of its leaf surface spectral curve (Figures 5 and 6). With the deepening of parasitic intensity, the degree of \"blue shift\" also increased, indicating that with the increase of parasitic intensity, the influence on the red edge of the leaf surface became more severe. In addition, the slope of the red edge of the host plant decreased obviously after parasitization with CK (0.01557) > T1 (0.01524) > T2 (0.01469) > T3 (0.01368)  
Figure 4: Spectral reflectance of healthy _Osmanthus fragrans_ leaves and spectral reflectance of _Osmanthus fragrans_ with different parasitic degrees. (Figures 5 and 6b). Many studies show that the red edge slope has a good indication of chlorophyll content [52]. Combined with Figure 3, with the deepening of parasitic intensity, chlorophyll content index is decreasing. Therefore, we suspect that the cause of this phenomenon was related to the influence of _Cuscutta japonica Choisy_ on the photosynthesis of host plants. As can be seen from Figures 5 and 6c, with the deepening of parasitic intensity, the spectral red valley reflectance of host plants Table 1 shows a trend of increasing at first and then decreasing (T1 (0.07912) > T2 (0.07153) > CK (0.0672) > T3 (0.0298)).