# _atmosphere_
## 3 Results
### Monthly Variations in CO\({}_{2}\) Fluxes  
Maximum monthly GPP occurred in July and August at both sites (Figure 5), and averaged 179.6 \(\pm\) 28.0 g C/(m\({}^{2}\) month) at LHZ and 161.6 \(\pm\) 11.0 g C/(m\({}^{2}\) month) at XBH. Similarly, maximum monthly RES averaged 97.2 \(\pm\) 6.0 g C/(m\({}^{2}\) month) at LHZ and 105.2 \(\pm\) 5.8 g C/(m\({}^{2}\) month) at XBH during July and August. The minimum monthly NEE averaged -82.4 \(\pm\) 24.3 g C/(m\({}^{2}\) month) at LHZ and -56.4 \(\pm\) 7.3 g C/(m\({}^{2}\) month) at XBH during these two months. Interestingly, the maximum monthly NEE occurred in November (47.5 \(\pm\) 3.2 g C/(m\({}^{2}\) month)) at LHZ, while it occurred in April (30.3 \(\pm\) 1.4 g C/(m\({}^{2}\) month)) at XBH, reflecting different hydrothermal conditions. The monthly RES at LHZ (56.1 \(\pm\) 27.2 g C/(m\({}^{2}\) month)) was significantly (\(p\) < 0.001) more than that at XBH (46.2 \(\pm\) 35.7 g C/(m\({}^{2}\) month)), in contrast to the undetectable difference in monthly GPP (\(p\) = 0.23) and monthly NEE (\(p\) = 0.10) at the two sites (Figure 6). Further analysis showed that the difference of RES mainly stemmed from an approximately two-fold larger non-growing season RES at LHZ (Figure 6b). Moreover, the nongrowing season RES comprised as much as 29.5% of the annual RES in LHZ, but only comprised 18.5% in XHB. During the growing season, both NEE and RES were significantly correlated with GPP, with 69.0% of the per-unit GPP contributed to RES and 31.0% to NEE. Monthly NEE at both sites was controlled much more by monthly GPP than by monthly RES, indicated by stronger standardized coefficients for the former (Figure 7). GPP and RES were both controlled by atmospheric water vapor and the direct effect was similar for both LHZ and XBH (0.78 versus 0.79 for GPP, and 1.01 versus 0.96 for RES) for the two wetlands. It should be noted that the indirect effect of atmospheric water vapor through EVI on CO\({}_{2}\) fluxes was significant (\(p\) < 0.05) at XBH alone, and the total effects of atmospheric water vapor on GPP and RES were 1.19 (0.79 + 1.09 \(\times\) 037) and 1.07 (0.79 + 1.09 \(\times\) 0.26), respectively (Figure 7b). This might be caused by XBH being a much lower EVI (Figure 1f). Therefore, the variations in monthly CO\({}_{2}\) fluxes were predominantly determined by monthly atmospheric water vapor during the growing season, and the effect of vegetation growth was important at XBH with lower plant coverage. GPP/RES, which evaluates the relative contribution of CO\({}_{2}\) exchange processes to the total CO\({}_{2}\) exchange, averaged 1.21 \(\pm\) 0.61 at LHZ and  
Figure 5: The monthly 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**)). 1.20 \(\pm\) 0.35 at XBH, respectively. The paired-sample t-test showed that the difference in GPP/RES between the two sites was non-significant (\(p\) = 0.91, N = 12). During the nongrowing season, monthly NEE was controlled by monthly \(T_{\rm s}\), and the relationship could be depicted by a \(Q_{\rm 10}\)-based model (\(NEE=a\times e^{\ln(Q_{\rm 10})(T_{\rm s}-10)/10}\), \(Q_{\rm 10}\) describes the proportional increase in the rate of respiration per 10 \({}^{\circ}\)C rise in temperature [5]; Figure 8). The reference respiration in LHZ was 29.8% more than that of XBH, while \(Q_{\rm 10}\) was 27.3% lower at the former site. Furthermore, the general linear model of monthly ln(NEE) with \(T_{\rm s}\) and site (categorical variable) revealed that the main effects of \(T_{\rm s}\) and site attributes were both significant (\(p<\) 0.001), but the interaction was insignificant (\(p\) = 0.91; Table S1). Thus, the nongrowing season monthly NEE should be jointly determined by \(T_{\rm s}\) and site attributes.