[M-IS05] Environmental, Socio-economic, and Climatic Changes in Northern Eurasia

[MIS05-P09] Soil organic carbon turnover in the meadow ecosystems of drained peatland (Tarmanskoe Fen, Western Siberia)

*Evgeniya Soldatova¹, Elizaveta Plotnikova¹ (1.Institute of Forest Science of the Russian Academy of Sciences)

Keywords:delta13C, isotopic approach , natural abundance, pasture, hayfield, rewetting

Evaluation of soil organic carbon (SOC) turnover rate is crucial for assessment of the measures targeted greenhouse gas (GHG) flux reduction and boosting C sequestration especially with drained wetlands. Drained wetlands are often subjected to rewetting for biodiversity restoration and climate change mitigation however the influence of such measures on GHG emission and C sequestration is debatable. We chose seven points in drained eutrophic Tarmanskoe Fen (south of the Western Siberia) subjected by the peat extraction in 70-80^th of XX century. There were four groups of points: 1. site naturally rewetted after peat extraction without reclamation due to earth surface decrease and degradation of drainage system; 2. point in the meadow which are occasionally used as a hayfield, and probably as a pasture and arable land; 3. the meadow which is used as a pasture and hayfield by local residents about 40 years. 4. Unoccupied meadows. The turnover rate of SOC was estimated based on stable isotope signatures (δ¹³C) down to 70 cm of the soil profile depth because the slope of the linear regression between δ¹³C and the logarithm of SOC is a proxy of SOM turnover (Acton et al., 2013; Powers and Schlesinger, 2002). Commonly, the SOC content logarithmically depends on depth, whereas the final ¹³C fractionation increases with the number of C cycles and with the intensity and completeness of the SOM processing according to the Rayleigh distillation. The regressions between the Lg-transformed SOC content and δ¹³C have negative linear trends. The negative slope (β_C) of the linear regression between Lg SOC and δ¹³C corresponds to the relative rate of C turnover (Wynn et al., 2006, 2005). Greater absolute values of β_C refer to higher relative SOC turnover rate. Content of SOC was measured by element analyzer varioPYROcube and δ¹³C was determined by isotope ratio mass-spectrometer isoprime precisION coupled with element analyzer varioISOTOPEcube (Elementar, UK) after removal of carbonates from soil sample by HCl fumigation. Surprisingly, we found that the rewetted plot has the highest SOC turnover rate compared to unoccupied meadows, hayfields and pastures (Fig. 1). However, all of the β_C values have the same order of absolute magnitude, near unity, which means relatively close SOC turnover within all studied plots. Only TMB-2 showed the β_C values close to zero and lowest SOC turnover rate. Correlation analysis showed that SOC turnover rate increases with SOC content in upper 30 cm of soil profile (rs 0.81, p<0.05) and decreases with soil compaction (with increasing of density (rs -0.74, p<0.05)). The connection with soil humidity is absent. It reflects faster loss of organic carbon from residual peat horizons and means that rewetting in this case do not prevent this process. Relative rate of SOC turnover also positively correlated with C content in aboveground biomass of the studied plots (rs 0.83, p<0.05) which can be a sign that more productive meadow ecosystems loss more organic carbon due to microbial respiration.
Research was supported by the Russian Science Foundation (No 23-77-10012).
References
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