## 4 Discussion
### Implications of the Local Soil Moisture Regimes for the CO\({}_{2}\) Exchange of Spruce Forests  
The hydrological regime of the site may be the key factor that determines the response of a forest ecosystem to climate extremes and anomalies. The results obtained from the flux measurements performed in the southern taiga memorose spruce forest were different from the results obtained from an old paludified spruce forest (Ru-Fyo FLUXNET ID) located 1.5 km from the study site [51]. While the ecosystem CO\({}_{2}\) uptake in the memorose spruce forest substantially increased in 2018, the annual GPP/TER ratio in the paludified spruce forest was less sensitive to the warm, dry, and sunny environmental conditions (Figure 7). Conversely, the CO\({}_{2}\) uptake of the paludified forest in 2020 increased significantly due to the anomalously warm conditions observed in winter and at the beginning of spring. The growing season TER at the paludified forest in 2020 decreased due to the high water levels seen in summer caused by a positive precipitation anomaly. In the memorose forest, the early start of the CO\({}_{2}\) uptake, as well as the TER dynamics, did not lead to an increase in the annual GPP/TER ratio. The annual sums of the CO\({}_{2}\) fluxes seen at the sites in the 2016-2020 period had a similar order of magnitude: NEE in the paludified forest varied between \(-95\pm 12\) and \(145\pm 41\) g\(\mathrm{C}\cdot\mathrm{m}^{-2}\), TER varied between \(1366\pm 92\) and \(1652\pm 44\) g\(\mathrm{C}\cdot\mathrm{m}^{-2}\), and GPP varied between \(1408\pm 45\) and \(1592\pm 112\) g\(\mathrm{C}\cdot\mathrm{m}^{-2}\), respectively [51]. However, the daily CO\({}_{2}\) fluxes in the memorose spruce forest varied within a wider range (Figure 8). This is likely connected with the high ground water level seen in the paludified spruce forest (close to the surface), which on the one hand, will mitigate the effect of the precipitation variability and preserve a consistent water supply in the soil, and on the other hand, create wet anoxic conditions and inhibit the respiration as well as productivity of spruce [11; 74]. Figure 7: (**a**) Mean annual GPP/TER ratio, (**b**) annual sums of the net ecosystem exchange (NEE), (**c**) total ecosystem respiration (TER) and (**d**) gross primary production (GPP) with the uncertainty estimates associated with random error in the measured fluxes: u*—threshold estimation, gap-filling, and flux partitioning procedures (\(\pm\)SD) in the paludified spruce forest (PF) [51] and the memorose spruce forest (NF, this study) in the 2016–2020 period. The comparison of the CO\({}_{2}\) fluxes observed in the two different southern taiga spruce forests in the growing seasons with the negative temperature and positive precipitation anomaly that occurred in 2017 and with the positive temperature and negative precipitation anomaly that occurred in 2018 showed that the TER at the memorose spruce forest was higher in the cool and wet year of 2017 (M-W U test, U = 12,275, Z = 4.42, \(p\) < 0.001), while the TER in the paludified forest was higher in 2018 (M-W U test, U = 13,955, Z = (\(-\)2.76, \(p\) = 0.006). The previous study conducted by [PERSON] et al. [69] reported that soil respiration is the major component of TER in paludified spruce forests. Additionally, it is likely that the soil respiration and TER of the memorose spruce forest in summer are limited by the water availability in the soil. In contrast, the soil respiration and consequently TER of the paludified forest is limited by soil aeration, which is generally low due to the high ground water levels. This may explain the different responses of the TER to the dry conditions experienced in summer 2018. However, in the case of a severe drought, a decreased TER in a paludified forest due to the water stress is very possible. Such an effect was observed in the paludified spruce forest during the extreme drought event that occurred in 2010 [69].