Carbon pools emissions in the soils of natural and post-agrogenic forest ecosystems and the dynamics of CO2 of the “BioCarbon” сarbon polygon (Novosibirsk)

In Western Siberia, studies on carbon pools in forest ecosystems, particularly regarding carbon dioxide emissions from natural and post-agrogenic forests, are extremely limited. Therefore, the aim of this study was to compare carbon pools and examine the dynamics of CO2 emissions in natural and secondary birch forests within the “BioCarbon” carbon polygon in Novosibirsk Oblast. The research was conducted from 2022 to 2024 on test areas of the “BioCarbon” carbon polygon located at the Central Siberian Botanical Garden site, under natural birch forest and approximately 20-year-old fallow land. The test areas (TA2, natural birch forest, and TA4, secondary birch forest) are situated within the transition zone from the upper floodplain terrace of the Ob River to the subaerial complex of the denudation-accumulative Pre-Salair plain (See Fig. 1). The soils are classified as Albic Luvisols (loamic) (See Fig. 2). Bulk density, porosity, and soil moisture content were determined using the thermostatic-weight method. Total carbon and nitrogen were measured at the ISSA SB RAS testing laboratory by dry combustion using a 2400 Series II CHN analyzer. Soil organic carbon (SOC) content was determined by wet oxidation with K2Cr2O7 in 50% H2SO4 solution. Carbon pools in soils were calculated for the 0-20, 0-50, and 0-100 cm layers. Carbon pools in the litter were measured using the frame-square method according to the Ministry of Natural Resources’ recommendations. CO2 fluxes from the soil surface were measured once monthly in the morning from May to September using a portable LI-COR 8250 infrared gas analyzer. During greenhouse gas flux measurements, soil temperature and humidity sensors were used at depths of 5-10 cm. The total carbon content in the studied soils varied within a relatively narrow range, not exceeding 2.3%. Notably, the soil under the natural forest exhibited a more pronounced decrease in soil organic carbon content with depth, whereas the agrogenically transformed soil at the TA4 site showed a gradual decrease in carbon content down the profile (See Table 1). The total carbon pool in the soil under the natural birch forest was 38 t/ha in the 0-20 cm layer and 46 t/ha in the 0-50 cm layer. In contrast, under the secondary birch forest, the total carbon pool was lower in the 0-20 cm layer (33 t/ha) but exceeded that of the natural soil in the 0-50 cm layer (62 t/ha). Conversely, the carbon pool in the litter was higher under the natural forest (2.2 t/ha) than under the secondary forest (1.8 t/ha). Over the two years of observation, average CO2 emissions were minimal in May (2.1-3.3 mol/m2s). The maximum CO2 flux from the soil surface under the natural birch forest occurred in July (13.3 mol/m2s), whereas under the secondary forest, the peak emission was observed in June (10.8 mol/m2s). By September, emission values declined again (See Fig. 3). Hydrothermal conditions in the topsoil varied across the test sites. Soil properties, which influence these conditions, affect the CO2 flux from the soil surface during the growing season. This relationship is demonstrated by the dependence of CO2 flux on temperature in the 0-5 cm soil layer over two years (See Fig. 4). Thus, the incorporation of infertile soils within the Novosibirsk Scientific Center into agricultural use has led to long-term changes in their properties. The agrogenic transformation of soil properties increases the sensitivity of soil respiration to changes in hydrothermal conditions and contributes to greater variability in CO2 flux over the years. The article contains 4 Figures, 1 Tables, 50 References. The Authors declare no conflict of interest.

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