## 3 Results
### The Relationships between Environmental Factors and CO\({}_{2}\)/H\({}_{2}\)O Fluxes  
The environmental factors affecting CO\({}_{2}\) and H\({}_{2}\)O fluxes during growing season in two forest ecosystems were different (Table 1). The results showed that SWC did not enter the multiple stepwise regression models in both of the two forest ecosystems, which meant that SWC had no significant effect on the CO\({}_{2}\) and H\({}_{2}\)O fluxes. The main impact factors of NEE, GPP, and ET are different for the two forest ecosystems. In the two forest ecosystems, NEE, GPP, and ET were influenced by PAR, while RECO was mainly affected by TA or TS and RH.  
Figure 3: Monthly variations (**A–D**) of CO\({}_{2}\) and H\({}_{2}\)O fluxes (net ecosystem exchange (NEE), ecosystem respiration (RECO), gross primary production (GPP), evapotranspiration (ET)), and hourly variations (**E–H**) of CO\({}_{2}\) and H\({}_{2}\)O fluxes (NEE, RECO, GPP, and ET) in two forest ecosystems. The value for each point in each panel represents the mean value and standard error during the whole analysis period.  
In order to better reveal the response of carbon (NEP, GPP, and RECO) and water fluxes (ET) to the significant environmental factors in the two forest ecosystems, the relationships between NEP, GPP, RECO, and ET and the significant environmental factors were fitted (Figure 4). The carbon and water fluxes had a linear relationship with PAR and VPD in the two forest ecosystems. The sensitivities of NEP, GPP, and ET to PAR in the _L. principis-rupprechtii_ and _P. tabulaeformis_ forest ecosystems were similar, and all showed a significant positive linear relationship (_p_ < 0.05) (Figure 4A,F,I). Similarly, the sensitivities of NEP, GPP, RECO, and ET to VPD in the _L. principis-rupprechtii_ and _P. tabulaeformis_ forest ecosystems also showed a significant positive linear relationship (_p_ < 0.05) (Figure 4B,D,G,J). However, the relationships between NEP, RECO, GPP, ET, and RH in the two forest ecosystems were not significant or weak (Figure 4C,E,H,K).  
In addition, the relationships between NEP, GPP, RECO, and ET and temperature (TA and TS) were established to investigate the response of CO\({}_{2}\)/H\({}_{2}\)O fluxes to temperature changes in two forest ecosystems (Figure 5). The NEP, GPP, and ET had significant exponential relationships with temperature (TA and TS) in two forest ecosystems, and the change rates of NEP, GPP, and ET in the _L. principis-rupprechtii_ forest ecosystem were larger than those in the _P. tabulaeformis_ forest ecosystem (Figure 5A,B,E-H). The temperature sensitivity (Q\({}_{10}\)) of RECO to TA in the _L. principis-rupprechtii_ forest ecosystem (Q\({}_{10}\) = 3.88) was higher than that in the _P. tabulaeformis_ forest ecosystem (Q\({}_{10}\) = 2.10) (Figure 5C). A similar pattern was found for the sensitivity of RECO to TS (Q\({}_{10}\) = 5.61 and Q\({}_{10}\) = 2.99) in the _L. principis-rupprechtii_ and _P. tabulaeformis_ forest ecosystems (Figure 5D). Furthermore, RECO was more sensitive to TS than TA in the same forest ecosystem (Figure 5C,D).  
Figure 4: The regression relationship between the daily CO\({}_{2}\)/H\({}_{2}\)O fluxes (NEP (negative NEE), RECO, GPP, and ET) and daily environmental factors (photosynthetic active radiation (**A**,**F**,**I**), vapor pressure deficit (**B**,**D**,**G**,**J**), and air relative humidity (**C**,**E**,**H**,**K**) in two forest ecosystems. (**A**–**H**) indicate different small panels.  
Figure 5: The regression relationship between the daily CO\({}_{2}\)/H\({}_{2}\)O fluxes (NEP (negative NEE), RECO, GPP, and ET) and daily environmental factors (air temperature (TA), soil temperature (TS)) in two forest ecosystems. (**A**–**H**) indicate different small panels.