## 4 Discussion
Consequently, SIF is expected to have a different performance to the other three vegetation proxies. However, keep in mind that a monthly time scale was considered here and that SIF values included in the same month were averaged in our analysis. Such processing conceals the characteristics of the high temporal resolution, e.g., 4 days, in SIF data, resulting in SIF having a similar performance to EVI and NDVI data here. Vegetation sensitivity in response to climate change exhibited pronounced spatiotemporal heterogeneity on the QTP for the four vegetation proxies. For both time-invariant and time-variant sensitivity, temperature was the most important factor regulating vegetation sensitivity of the QTP over the last two decades, which is consistent with the findings of [PERSON] et al. [1], [PERSON] et al. [2], [PERSON] et al. [6], and [PERSON] et al. [24]. Our results revealed that temperature generally exerted positive impacts on vegetation sensitivity for the high-cold grasslands located in the central to eastern QTP, which was also reported in the study by [PERSON] and [PERSON] [61]. However, our results also demonstrated that vegetation of the QTP experienced a downward trend in the sensitivity to temperature variability, indicating that the impact of temperature on vegetation is gradually decreasing. In particular, [PERSON] et al. [62] pointed out that such declining phenomena reflect a shift from water to energy limitations for vegetation of the QTP. Moreover, the declining trend may be attributed to the acclimation of plants and communities, such as plant biomass allocation and changes in community composition, so that vegetation on the QTP [63; 64; 65] can cope with the widespread global warming. We found solar radiation to be an important climate factor that should not be ignored in vegetation sensitivity studies, which has also been emphasized recently by [PERSON] et al. [22], [PERSON] et al. [24], and [PERSON] et al. [37]. The trend analysis showed that forests in the southeastern QTP displayed an increasing sensitivity to solar radiation. As temperature is continuously increasing in the southeastern QTP [6], solar radiation modifies forest sensitivity by stimulating photosynthesis and makes forests absorb more carbon dioxide. By contrast, grasslands and BSVs appeared to show declining sensitivity in response to solar radiation, and solar radiation exerted negative impacts on grasslands and BSVs. This may be explained by the fact that high levels of solar radiation on the QTP make plants reach their light saturation points easily by regulating leaf nitrogen and phosphorus stoichiometry, which leads to the photoinhibition of photosynthesis [66]. Compared with temperature and solar radiation, all four vegetation proxies revealed a small temporal trend for vegetation sensitivity in response to water availability on the QTP in the last two decades. Such phenomena were more pronounced in central to eastern areas of the QTP, where the trend values for grasslands were small, which may be explained by their elevations. By contrast, forests and BSVs exhibited upward trends regarding water availability, which is consistent with the findings of [PERSON] et al. [65] and [PERSON] et al. [17] and may be related to the human-environment nexus [13] through grazing, farming, and urbanization [50]. Over the last two decades, water availability generally exerted positive impacts on vegetation sensitivity, except for the forests located in the southeastern QTP. Forested areas are more sensitive to water availability than temperature and solar radiation,and they displayed positive sensitivity trends. This may occur as a consequence of climate warming and persistent drought in these areas [67; 68]. In addition, [PERSON] et al. [4] pointed out that precipitation impacts on vegetation spring phenology on the QTP, especially in the drylands, which may alter the vegetation sensitivity on the QTP accordingly.