Processes involving soil CO2 dynamic in a sector of Chaco-Pampean plain, Argentina: An isotope geochemical approach

The magnitude and spatial variability of CO 2 surface emissions and processes involving CO 2 released to the atmosphere from the soils are relevant issues in the context of climate change. This work evaluated CO 2 fluxes and 13 C/ 12 C ratio of vegetation, organic matter, and soil gases from no disturbed soils of Chaco Pampean Plain (Argentina) with different soil properties and environmental conditions (PL and PA units). Soil organic decomposition from individual layers was accompanied by δ 13 C of total organic carbon (δ 13 C-TOC) values more enriched to depth. δ 13 C-TOC values in the upper soil profile ~ ca. 0–15 cm were like the plant community of this area (~−33 to −29 ‰) while δ 13 C-TOC varied stronger bellow horizon A, till ~ −24‰. Both δ 13 C-TOC and soil δ 13 C-CO 2 were similar (~ −24 to 26 ‰) at deeper horizons (~ 50–60 cm). Toward the superficial layers, δ 13 C-TOC and δ 13 C-CO 2 showed more differences (till ~ 4 ‰), due influence of the diffusion process. Horizon A layer (~ 0–20 cm) from both PL and PA units contained the most enriched δ 13 C-CO 2 values (~ −15–17 ‰) because atmospheric CO 2 permeated the soil air. A simple two-component mixing model between sources (atmospheric δ 13 C-CO 2 and soil CO 2 ) confirmed that process. Isotopically, CO 2 fluxes reflected the biodegradation of C3 plants (source), diffusive transport, and CO 2 exchange (atmosphere/soil). Soil moisture content appeared as a determining factor in the diffusion process and the magnitude of CO 2 surface emissions (12–60 g·m −2 ·d −1 ). That condition was confirmed by CO 2 diffusion coefficients estimated by air-filled porosity parameters and soil radon gradient model.