## 3 Results
### SIF Characteristics  
As illustrated in Figure 7, the spatial distributions of the CSIF, GOSIF, and RTSIF during the GS were similar. The SIF values were relatively high in the eastern and southern parts of the TRHR (CSIF and GOSIF reaching 0.2 mW\(\cdot\)m\({}^{-2}\cdot\)nm\({}^{-1}\cdot\)sr\({}^{-1}\), with RTSIF reaching 0.3 mW\(\cdot\)m\({}^{-2}\cdot\)nm\({}^{-1}\cdot\)sr\({}^{-1}\)), whereas they were relatively low in the western parts of the region (CSIF and GOSIF below 0.05 mW\(\cdot\)m\({}^{-2}\cdot\)nm\({}^{-1}\cdot\)sr\({}^{-1}\), and RTSIF below 0.1 mW\(\cdot\)m\({}^{-2}\cdot\)nm\({}^{-1}\cdot\)sr\({}^{-1}\)). The correlation coefficients of the annual GS-averaged GOSIF GPP with CSIF, GOSIF, and RTSIF, respectively, were high--especially in eastern parts of the TRHR (>0.9). These results together indicate that SIF effectively captures vegetation photosynthesis dynamics.  
The annual GS-averaged SIF showed increasing trends during 2001-2020 (Figure 8), which was especially the case for GOSIF (0.0068 mW\(\cdot\)m\({}^{-2}\cdot\)nm\({}^{-1}\cdot\)sr\({}^{-1}\cdot\)decade\({}^{-1}\)). This suggests that vegetation greening significantly increased in the TRHR during those years. The annual variations in GPP and SIF were more consistent, with a trend value of 4.12 gC\(\cdot\)m\({}^{-2}\cdot\)month\({}^{-1}\cdot\)decade\({}^{-1}\). The correlation coefficients of GPP and the three types of SIFs exceed 0.9 on the annual timescale, indicating that SIF responds well to GPP characteristics in the TRHR.  
The spatial characteristics of the three distinct SIF trends exhibited a consistent pattern across the TRHR (Figure 9), with positive trends in most areas and especially in the northeastern parts of the region (0.05 mW\(\cdot\)m\({}^{-2}\cdot\)nm\({}^{-1}\cdot\)sr\({}^{-1}\cdot\)decade\({}^{-1}\)). The TRHR shows far more areas with significant greening than those with significant browning trends in terms of vegetation areas, especially in the east-central areas. These observations indicate enhanced photosynthetic capacity in the TRHR's vegetation. There were fewer areas with significant greening in the RTSIF dataset than in CSIF or GOSIF datasets, especially in the western parts of the region.  
The annual mean temperature and precipitation in the TRHR trended upward (Figure 10a), reaching 0.34 \({}^{\circ}\)C/decade and 33.04 mm/decade, respectively, indicating that warming and wetting have become more pronounced in the TRHR over the past two decades. The variations in the GS temperature and precipitation (Figure 10b) were similar to those occurring on the annual scale, but with a more intense warming of temperature (0.42 \({}^{\circ}\)C/decade). Grass grew more prolifically under these warmer and wetter conditions in the TRHR, which supports the significant increases in the SIFs observed previously.  
Figure 7: Spatial distribution of mean (**a**) CSIF, (**b**) GOSIF, and (**c**) RTSIF during GS from 2001 to 2020. Relationships between GPP and (**d**) CSIF, (**e**) GOSIF, and (**f**) RTSIF at annual GS timescale.  
Figure 8: Annual GS changes in CSIF, GOSIF, RTSIF, and GOSIF GPP anomalies in the TRHR during 2001–2020.  
Figure 9: Spatial GS trends of (**a,b**) CSIF, (**c,d**) GOSIF, and (**e,f**) RTSIF in the TRHR during 2001–2020. Trend significance identified at \(p<0.05\).