# _atmosphere_
## 3 Results
### Eight-Day Variations in CO\({}_{2}\) Fluxes  
The trends of seasonal CO\({}_{2}\) fluxes were similar at the two sites, although the magnitudes were to some extent different (Figure 2). Daily GPP averaged 3.23 \(\pm\) 1.88 g C/(m\({}^{2}\) d) (Mean \(\pm\) S.D., the same below) at LHZ and 3.43 \(\pm\) 2.25 g C/(m\({}^{2}\) d) at XBH. The paired-sample t-test showed that the difference was marginally significant (\(p\) = 0.07). Daily RES was 1.83 \(\pm\) 0.90 g C/(m\({}^{2}\) d) at LHZ, which was significantly (\(p\) < 0.001) more (by 17.6%) than that of XBH. Therefore, daily NEE was 0.11 \(\pm\) 1.57 g C/(m\({}^{2}\) d) at LHZ, and this was much higher than that of XBH (-0.11 \(\pm\) 0.96 g C/(m\({}^{2}\) d)).  
During the growing season, the mean total deviance and 10-fold cross-validation deviance for 8-day GPP, RES, and NEE were 108.57 and 9.67, 72.14 and 3.47, and 269.57 and 17.64, respectively, which suggested the good performance of the BRT models (\(R^{2}\) > 0.90, Figure S3). The results showed that the variations of 8-day GPP and 8-day NEE were mostly determined by atmospheric water vapor, with relative contributions of more than 65% (Figure 3a). GPP showed a positive correlation with atmospheric water vapor, while NEE showed a negative correlation with atmospheric water vapor (Figure 4a,d). Variations in 8-day RES were jointly controlled by atmospheric water vapor and \(T_{\rm s}\), which explained 76.5% of the total variations. RES showed a positive correlation with both atmospheric water vapor and \(T_{\rm s}\) (Figure 4b,c). It should be noted that the relative contribution of site (categorical variables) was less than 2%, which indicated that the growing season patterns of 8-day CO\({}_{2}\) fluxes at the two sites should be attributed to variations in environmental controls rather than site attributes. Furthermore, the contribution of EVI to NEE was more than 10%, although it was only 5.0% for GPP and 9.8% for RES (Figure 3a).  
During the nongrowing season, the mean total deviance and 10-fold cross-validation deviance for 8-day NEE were 9.57 and 2.59 (\(R^{2}\) = 0.73; Figure S3), respectively. The variability in NEE was jointly determined by site attributes and \(T_{\rm s}\), with cumulative relative contributions of 81.8% (Figure 3b). Mean daily NEE was approximately 1.07 \(\pm\) 1.57 g C/(m\({}^{2}\) d) at LHZ, which was about twice that of XBH (0.56 \(\pm\) 0.96 g C/(m\({}^{2}\) d), Figure 4e). NEE exponentially increased with \(T_{\rm s}\) at both sites (Figure 4f).  
Figure 2: The 8-day variations in CO\({}_{2}\) fluxes of the two alpine wetlands (gross primary productivity GPP, **(a)**; ecosystem respiration RES, **(b)**; net ecosystem CO\({}_{2}\) exchange NEE, **(c)**).  
Figure 4: The fitted 8-day CO\({}_{2}\) fluxes (net ecosystem exchange NEE, **(a,e,f)** ecosystem respiration RES, **(b,c)** gross primary productivity GPP, **(d)** in relation to each of the important predictors (Vapor: atmospheric water vapor; \(T_{\rm s}\): topsoil temperature) used in the model during the growing season (**a,d**) and nongrowing season (**e,f**).  
Figure 3: The relative contributions of environmental controls on variations in the growing season (**a**) and the nongrowing season (**b**) 8-day CO\({}_{2}\) fluxes of the two alpine wetlands.