## 3 Results  
Meteorological and environmental conditions were quite different for the two eddy covariance stations located in the two different climate zones. Since the Kursk field is 600 km south of the Moscow field, higher daily PPFD values were observed for the Kursk field. Summertime modal PPFD values were 600 umol m\({}^{-2}\) s\({}^{-1}\) and 400 umol m\({}^{-2}\) s\({}^{-1}\) for the Kursk and Moscow fields, respectively (Figure 2a). Nevertheless, daily and seasonal temporal PPFD patterns were similar for both fields. Daily PPFD reached its maximum three times: at the end of May, at the end of June and at the middle of August. There was a sharp decline after the first maximum for a week in mid-June that is typical for the European part of Russia. The average 7-day PPFD started to decrease gradually after the end of August. Minimal average monthly PPFD was registered at both sites during November-December (18 umol m\({}^{-2}\) s\({}^{-1}\)) and maximal ones were detected in June (414 umol m\({}^{-2}\) s\({}^{-1}\)) at the Moscow site, and in July (659 umol m\({}^{-2}\) s\({}^{-1}\)) at the Kursk site. The difference in mean soil temperature at a 5 cm depth was significant for both fields (Figure 2b). The average monthly soil temperature at a 5 cm depth was higher than 15 \({}^{\circ}\)C from May to August at the Moscow site, and from April to August at the Kursk site. Monthly precipitation (mm) is presented in Figure 2c. The total precipitation during the growing season was about 200 mm at the Moscow site and about 120 mm at the Kursk site; it is approximately one-third and one-fifth of the total precipitation per year, respectively. The amount and dynamics of precipitation and corresponding soil water content at the studied plots differed distinctly. During the first part of the growing season soil water content (SWC) at the Kursk field was higher, due to the better moisture-retention capacity of chernozem (Figure 2c). The peak of SWC detected at the Kursk field was associated with heavy rain in mid-May. For the Moscow field, the highest SWC was detected at the end of vegetation season in response to repeated rain events. The NEE diurnal patterns clearly showed significant inter-seasonal and inter-site differences (Figure 3). Diurnal patterns of NEE were considerably higher in amplitude for the Kursk site, which reached the highest NEE peak in May and June. For the Moscow field, NEE values were about zero during March, when the soil was covered with snow. Snowmelt in mid-April did not change the NEE diurnal dynamic much. CO\({}_{2}\) fluxes  
Figure 2: Seasonal variations of (**a**) daily mean photosynthetic photon flux density, \(\mu\)mol\(\cdot\)m\({}^{-2}\cdot\)s\({}^{-1}\) (PPFD), (**b**) daily soil temperature at 5 cm depth C\({}^{\circ}\) (Isoil), (**c**) daily precipitation sum (mm) and daily mean volumetric soil water content (SWC) at 5 cm depth, during the growing season and the end of the year (from the end of April to the mid of September) at the eddy covariate station at Moscow (dark dots, solid lines and black bars) and station at Kursk (empty dots, dashed lines and grey bars). increased after crop emergence in May. The Kursk site showed similar uptake values and dynamics in both May and June. In May, the higher diurnal differences between sites were driven by different crop development stages: in Moscow the phonological phase was from seedling to tillering, while it was milky-wax ripeness in the Kursk field. Maximum CO\({}_{2}\) uptake was observed in June, with average values about \(-15\)\(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\) and \(-7.5\)\(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\) for the Kursk and Moscow fields, respectively.