## 4 Discussion
### Climatic and biotic Control over RE  
Climatic conditions regulate the spatiotemporal patterns and variation in RE [1; 66]. Temperature is the main factor affecting the RE rate in the absence of other environmental stresses [67]. This is because respiration requires the catalysis of enzymes, and temperature is a necessary condition for enzyme decomposition [68]. According to our results (see Section 3.3.2), warming promoted an increase in RE in alpine grasslands across the four alpine grassland subtypes as well as within the same subtype. It did not lead to an increase in RE in temperate grasslands, and even led to a decrease in RE in TS and DS (Figure 8a). Warming had no effect on RE, which may be related to the limited precipitation in temperate grasslands (Figure S3b) that restricts plant production and microbial activity [69]. This also indicates that warming can increase the RE under favorable environmental conditions when moisture availability is not a restrictive factor. PRE provides the necessary water for vegetation growth, affecting canopy structure and plant production [70], and ultimately improves autotrophic respiration. PRE changes the soil microenvironment, affecting the dissolution and diffusion of organic solutes, gases, and enzymes [67; 71]. This promotes microbial activity [72], and improves heterotrophic respiration. However, a saturation phenomenon affects RE under conditions of high precipitation (Figure 7b), which has been reported in previous studies [13; 27]. This may be because precipitation in excess of the saturated soil moisture reduces the oxygen content in the soil [27; 68]. It also inhibits the activity of plant roots and aerobic microorganisms, and reduces RE in grasslands. The different levels of saturated PRE for RE in alpine grasslands and temperate grasslands may reflect differences in the water requirements for different vegetation types. The increase in the annual total PRE, and not the annual average Ta, had a positive effect on the annual RE within the same temperate grassland subtype (Figure 8a,b). This may be associated with the greater increase in precipitation than in temperature from \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Model** & \(\mathbf{R^{2}}\) & **RMSE** & **References** \\ \hline T\&P & 0.68 & 1.23 & [1] \\ RECO & 0.63 & 0.97 & [16] \\ Satellite-Based Model & 0.75–0.79 & 0.60–0.77 & [12] \\ BP\_ANN & 0.84 & 0.51 & [34] \\ SVR & 0.85 & 0.49 & [34] \\ RF & 0.84 & 0.50 & [34] \\ SAE & 0.86 & 0.47 & [34] \\ Geoman & 0.87 & 0.39 & This study \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The accuracy performance of different models. 2001-2015 (Figure S3a,b). The annual average Ta had a greater stimulating effect on the increase in annual RE in the same alpine grassland subtype (Figure 8a), which was associated with the increase in the annual average Ta (Figure S3a). These results illustrate that PRE and Ta were the dominant climatic factors for interannual changes in RE in temperate grasslands and alpine grasslands, respectively. IM temperate grasslands are mainly distributed in arid and semi-arid zones, and limited moisture strongly restricts vegetation growth and microbial activity, which each affect RE changes [34]. Although plants that grow in alpine regions have adapted to the low temperature environment, their production and respiration processes are comparatively restricted. A minor temperature rise can contribute to an increase in RE by prompting the grassland to turn green, and increasing the biomass, the microbial activity, and litter decomposition [73; 74; 75]. The promoting effect of PAR on RE at the seasonal scale can be attributed to the effect of the seasonal PAR cycle on photosynthesis. Stronger photosynthesis tends to mean stronger respiration. However, at the interannual scale, the influence of annual PAR on annual RE changes was not significant in the alpine grasslands nor in the temperate grasslands (Figure 8d), which may be related to the long-term stability of solar radiation (Figure S3d).