## 3 Results and Discussion
### The Response of NEE and LE Fluxes to the Extreme Temperature Anomalies
#### 3.1.1 Variation in NEE and LE Flux in Warm Season
The number of cases where the anomalies of temperature and NEE/LE were observed on the same day is shown above the bars. Figure 8: The percentage of days when NEE and LE anomalies greater than 1 STD occurred simultaneously with extremely high (**a**) and low (**b**) temperatures during the warm season in mixed and evergreen broadleaf forests (see text for details). The number of cases where the anomalies of temperature and NEE/LE were observed on the same day is shown above the bars. Figure 9: The percentage of days when NEE and LE anomalies greater than 1 STD occurred simultaneously with extremely high (**a**) and low (**b**) temperatures during the warm season in deciduous broadleaf and needleleaf forests (see text for details). The number of cases where the anomalies of temperature and NEE/LE were observed on the same day is shown above the bars. Extremely high temperatures were also accompanied by positive anomalies of LE (green bars in Figures 7-10) due to the intensification of evaporation processes with increasing temperature. This relationship was observed in all forest types considered (Figures 7a, 8a and 9a). At the same time, as shown in Figure S4.2, the temperature increase led to growth in LE anomalies. Negative LE anomalies (yellow bars in Figures 7-10) during the hot periods were very rare (less than 10% of days). The cold periods occurring during the warm season mostly induced strong negative LE anomalies (Figures 7b, 8b and 9b) due to the suppressed evaporation at low temperatures [69]. The temperature decrease resulted in a reduction in negative LE anomalies (Figure S4.2). The response of NEE fluxes to negative temperature anomalies varied significantly among forest types and even among forests within a forest biome, depending on forest species composition, forest location, and landscape characteristics (Figures 7-9, Figures S5.3 and S5.4). At three stations located in mixed forests and at the FR-Pue station, located in evergreen broadleaf forests (Figure 8b), CO\({}_{2}\) uptake (blue bars) increased with decreasing temperature, indicating more favorable conditions for photosynthesis at relatively low summer temperatures. However, positive NEE anomalies, associated with higher CO\({}_{2}\) release (red bars), occurred more frequently than negative ones at most of the stations located in evergreen coniferous forests (Figure 7b) and in deciduous broadleaf and needleleaf forests (Figure 9b). This effect may lead to several causes and may be closely related to local microclimate and soil moisture conditions [19]. Thus, the positive and negative temperature anomalies in both evergreen coniferous forests and deciduous broadleaf and needleleaf forests resulted in prevailing positive NEE anomalies. The temperature effect on NEE and LE fluxes during the warm season did not differ significantly between boreal and temperate forests, with similar controlling mechanisms involved. Under positive temperature anomalies, it may be determined by suppressed assimilation processes due to high temperature and insufficient soil moisture [70; 71; 72], as well as a higher decomposition rate of soil organic matter and higher  
Figure 10: The percentage of days when NEE and LE anomalies greater than 1 STD occurred simultaneously with extremely high (**a**) and low (**b**) temperatures during the cold season in mixed evergreen broadleaf, deciduous broadleaf, and needleleaf forests (see text for details). The number of cases where the anomalies of temperature and NEE/LE were observed on the same day is shown above the bars. autotrophic respiration [21]. Under negative temperature anomalies, it may be caused by a large reduction in GPP at lower temperatures [73]. Comparing the effect of positive and negative temperature anomalies on NEE and LE, we can see that extremely high temperatures had a stronger effect on NEE and LE fluxes than air temperature decreases during the warm season (Figures 8 and 9).