## 2 Materials and Methods  
### The Sites, Measurements, and Soil Properties  
The research is focused on two forest ecosystems situated on the opposite banks of Oka River near Pushchino town, Moscow region. The first site (54\({}^{\circ}\)50\({}^{\prime}\) N, 37\({}^{\circ}\)35\({}^{\prime}\) E) with the sandy Entic Podzol (Arenic) [50] is located in the zone of coniferous-deciduous forests in Prioksko-Terrasny Nature Biosphere Reserve on the left (northern) bank of Oka River (top, Figure 1). The landscapes are plain sandy terraces formed as the result of modern and ancient erosion processes located above Oka-River flood plain--the low plains with the gentle southern slopes toward the River. The second site (54\({}^{\circ}\)20\({}^{\prime}\) N, 37\({}^{\circ}\)37\({}^{\prime}\) E) with the loamy Haplic Luvisol (Siltic) [50] is located in the zone of deciduous forests on the right (southern) bank of Oka River (bottom, Figure 1). The landscape is hilly with about 150-m of elevation above the River. Oka River serves as the boundary between the forest zones. The cross distance between the sites is about 8.6 km in the north-south direction. Both forest sites are located in the same moderately-continental climate zone with warm summers and moderately cold winters. Long-term meteorological observations (the Complex Background Monitoring Station, settlement of Danki, Serpukhov district, Moscow  
Figure 1: Study sites, soil profiles (Entic Podzol and Haplic Luvisol) and site locations on the opposite banks of Oka River; Prioksko-Terrasny Reserve is north from the River (“Prioksko-Terrasny Reserve”, 54\({}^{\circ}\)52\({}^{\prime}\) N, 37\({}^{\circ}\)35\({}^{\prime}\) E, Google Earth. November 2021. 25 May 2023); top left—Entic Podzol and bottom left—Haplic Luvisol soil profiles. region; \(54^{\circ}50^{\prime}\) N, \(37^{\circ}35^{\prime}\) E) for the last 10 years ([[https://pt-zapovednik.org](https://pt-zapovednik.org)]([https://pt-zapovednik.org](https://pt-zapovednik.org)), accessed on 1 June 2023) report the following: the average annual air temperature is 4.8 \({}^{\circ}\)C, the average summer temperature is +17.6 \({}^{\circ}\)C (max 38-39 \({}^{\circ}\)C), and the average winter temperature is \(-8.3\)\({}^{\circ}\)C (min \(-43\)\({}^{\circ}\)C in 1978); the average precipitation is 671 mm (max 91 mm in July); the duration of the seasonal snow cover period is 133 days with the average snow depth being 52 cm; the vegetation season lasts 186 days. Due to the specifics of geomorphology, the soil properties of these sites are quite different (left, Figure 1; Table 1). The higher concentration of fine particles (silt and clay) in the Haplic Luvisol and consequently, smaller pores, explain its higher water-holding capacity and as the result is the lower permittivity to the atmospheric oxygen, reducing _SOC_ oxidation [36], which is directly associated with its higher carbon storage. This process is well investigated on the examples of the wet-meadow and bog soil, having high _SOC_ storage as well [26; 37; 43; 51]. For the current research, we use a 25-year-long SR-measurement time series conducted by the chambers of the closed type (SR--top, Figure 2) once a week. The standard chamber-measurement approach is described in [20]. Firstly, the repetitive with 10-min interval gas measurements using syringe-sample collection are conducted at sites at five nearby locations to account for SR heterogeneity. Secondly, these samples are analyzed for CO\({}_{2}\) concentrations in the laboratory using a gas chromatograph (KrystaLIyuks-4000 M, MetaChrom, Yoshkar-Ola, Russia). The obtained changes in CO\({}_{2}\) concentration are recalculated into the SR fluxes by applying the chamber volumetric correction [19; 22]. Simultaneously with the SR, the soil temperature at 5-cm depth and the air temperature at 1-m height were measured at the sites (\(T_{soil}\)--brown, \(T_{air}\)--red; middle, Figure 2).