## 4 Discussion
### Response of Climatic Sensitivity of Vegetation Indices to MJP  
In this study, we found the temperature sensitivity of the mid-growing season vegetation indices in the meadow consistently and significantly increased (\(p<0.01\)) while precipitation sensitivity decreased (\(p<0.01\)) with the increase in the early growing season (May-June) precipitation (MJP) (Figure 6a,c,e,g). We assumed that more precipitation in the early growing season (May-June) may be an antecedent signal of a wet mid-growing season, which means that more MJP is an indicator of more coming JAP (precipitation in July-August) thus a wet year is well-deserved. Thus, more JAP would enhance the temperature sensitivity of vegetation indices and lower the precipitation sensitivity of the meadow. However, we examined the relationship between MJP and JAP, and the relationship was indistinct and insignificant (\(p>0.1\); not shown). It is widely recognized that, besides the climate factors, the acclimation of plant and community, such as plant biomass allocation and community composition changes, is also an important biotic factor regulating the relationship between climate and vegetation functions [1,3,15,69]. More MJP may be the result of higher surface evapotranspiration (ET) at the expense of soil water. It may induce soil \"drought\" and affect the biomass allocation (more biomass in root) and community composition (dominance of xeric and mesic species) during the early growing season, which probably enhances the water acquisition capacity of the meadow in the mid-growing season and consequently increases the temperature sensitivity but decreases the precipitation sensitivity (Figure 6a,c,e,g). Indeed, we found a negative correlation between precipitation and soil moisture in May (Figure 7a), and precipitation in June had no significant effect on the soil moisture of each layer in June (Figure 7b). We also examined the relationship between monthly mean surface ET and the top four layers of soil moisture in May-June, and it was proved to be negative; meanwhile, the relationship between ET and 0-28 cm depth soil moisture was statistically significant (\(p<0.05\)) (Figure 8a). In contrast to the meadow, the correlation was positive for the ET and soil moisture on the steppe, and the relationship between ET and the top layer soil moisture was notably (\(p<0.05\)) (Figure 8b). In addition, we also examined the spatial and temporal correlation between MJP and ET over the alpine meadow, and the results showed that MJP and ET were positively correlated in nearly 70% of the areas (by counting the number of pixels), and more than 60% of the areas reached the statistical significance level (\(p<0.05\)). Temporally, for ET and precipitation in May overall the meadow positivity correlated (\(R=0.38\), \(p<0.1\)), while the relationship is indistinct in June (\(R=0.19\), \(p=0.42\)). Thus, more ET might cause a higher MJP in the early growing season. Previous studies also showed that plant biomass allocation or community composition changes responded to climate change. For example, with 164 published studies, [PERSON] et al. [22] showed that drought significantly increases the root mass and decreases the allocation of biomass in the stem and leaf. For a semiarid temperate steppe in Inner Mongolia, it was proved that the community composition was dominated by precipitation  
Figure 8: Relationship between monthly mean evapotranspiration (ET, mm) and soil moisture content (m\({}^{3}\) m\({}^{-3}\)) in May–June in the meadow (**a**) and the steppe (**b**). The color lines indicate the least-squares fit between ET and soil moisture in each depth (red: 0–7 cm; blue: 7–28 cm; yellow: 28–100 cm; green: 100–285 cm) and the corresponding \(p\) indicates the significance level. through changes soil moisture [17]. On the TP, based on 4-year drought manipulation on the meadow in the TP, it was also proved that drought manipulation truly shifted more NPP allocation belowground because a developed root system promotes the ability of vegetation to obtain water [3].