## 4 Discussion  
### Variability of Re Components  
Our results showed that Ra/Re (1 - \(\beta^{*}\gamma\)) was not constant, but with a distinct seasonal variation throughout the growing season in this alpine meadow. The contribution of Ra to Re rises with spring warming and generally reaches the maximum value in the vigorous growth period, then declines with autumn cooling [9; 49; 78; 79; 83; 84]. Although research on Rs/Re (\(\gamma\)) also showed a distinct seasonal pattern similar to Ra/Re before the summer, this ratio increased again in the following autumn [78; 85]. Different trends between the two ratios might ascribe to different controlling mechanisms. Specifically, the Ra/Re was mainly followed plants' photosynthetic capacity from the phonological stages and was generally coupled with the seasonality of temperature and moisture [9; 86]. However, the Rs/Re was mainly controlled by the availability of stored substrates and the lags between temperature changes of air and soil [78]. The heterotrophic contribution to Rs (\(\beta\)) is relatively robust and showed only a negligible seasonal pattern compared to Ra/Re (1 - \(\beta^{*}\gamma\)) and Rs/Re (\(\gamma\)) [9; 81; 84; 85], because both autotrophic and heterotrophic respiration increased with seasonal warming [9].  
In this study, chamber-based Rm/Rs (\(\beta\)) generally ranged from 0.40 to 0.80 with two obvious exceptions around 0.2, which were measured on 24 August and 4 September 2010 (Figure 7a). These two days both had extremely high SWC caused by consecutive strong rainfall events (Figure 3), which dramatically stimulated the autotrophic contribution to Re due to the significantly positive relationship between SWC and Ra/Re (\(p<0.0001\)) (Figure 8). Many relevant studies also suggest that high SWC has a more significant effect on plant activity than on soil microorganisms [84]. Meanwhile, extremely high SWC inhibited Rm from deep soil layers due to the water block of soil porosity [87], and limited the oxygen supply for decomposition by aerobic microbes [88]. Besides, root exclusion was likely to intensify soil moisture due to a decrease of transpiration under this extremely wet condition [12; 84]. Although these pulse effects were not detected by satellite-based Ra/Re (Figure 7b), the daily SWC in this semiarid alpine meadow was generally less than 0.25 (Figure 3). In addition, any other chamber-based measuring dates were selected at least two days after a rainfall event [47]. Therefore, to avoid the impacts of pulse effects and ensure the comparability with other chamber-based measurements, these two measurements were assumed to be abnormal and excluded from further analysis.  
Figure 8: The effect of soil water content (SWC) on the ratio of autotrophic respiration (Ra) and ecosystem respiration (Re) (1 - \(\beta^{*}\gamma\)). CAM is derived from the camber-based Re components measurements. MODM is estimated from satellite-based Re partitions. The red dots are abnormal measurements due to the high moisture condition. The red solid and dashed curves are the best fitted lines for the relationship between camber-based and satellite-based 1 - \(\beta^{*}\gamma\) and SWC, respectively. The shadows are the 95% confidence bands for corresponding fitting curves.  
In the growing season during 2009 to 2011, our results showed that autotrophic contribution to Re (Ra_EC/Re_EC) ranged from 0.27 to 0.56, which fell within the range of similar alpine ecosystem in Qinghai [83] and Tibet [45] (Table 4). However, it was slightly lower than that of an alpine meadows in Haibei [79], which might be mainly caused by the significant lower biomass (91.9 g drought weight (DW) m\({}^{-2}\)) in this site than Haibei with biomass of 355.7-512.4 g DW m\({}^{-2}\) in 2009 [79]. Meanwhile, the inter-annual variation of Ra_EC/Re_EC showed that the year 2009 had a lower autotrophic contribution to Re (Ra_EC/Re_EC) (0.27) than the latter two years (0.50), which attributed to the most drought and lowest vegetation conditions (NDVI) in 2009 (Figures 3, 4 and 8).