Temperature controls diel oscillation of the CO2 concentration in a desert soil

Abstract

The diel dynamic of the CO2 concentration in soils in relation to temperature is not yet fully understood. Air temperature might control the soil CO2 concentration due to thermal convective venting at sites experiencing large temperature differences between the atmosphere and the soil. Therefore, the objective of this study was to determine the soil CO2 concentration and its temporal dynamic in a deep desert soil in relationship to soil and air temperature based on high frequency measurements. For this purpose, CO2 concentration and temperature were measured in six soil depths (ranging from 15 to 185 cm) in a coarse-textured desert soil in the North of Chile every 60 min together with precipitation and air temperature for one year. The mean CO2 concentration calculated across the whole measuring period increased linearly with soil depth from 463 ppm in 15 cm to 1542 ppm in 185 cm depth. We observed a strong diel oscillation of the CO2 concentration that decreased with soil depth and a hysteretic relationship between the topsoil CO2 concentration and both air and soil temperature. The Rayleigh-Darcy number calculated for different times indicates that thermal convective venting of the soil occurred during the night and in the early morning. A small precipitation event (4 mm) increased the CO2 concentrations in 15, 30, and 50 cm depths for several days but did not alter the amplitude of the diel oscillation of the CO2 concentration. The diel oscillation of the CO2 concentration and the hysteretic relationship between soil CO2 concentration and air temperature were likely caused by thermal convection, leading to transport of CO2-rich air from the soil to the atmosphere at night. In conclusion, our results indicate that the soil CO2 concentration can be largely controlled by convection caused by temperature differences, and not only by diffusion. The results have important implications as they provide further evidence that thermal convective venting contributes to gas exchange at sites experiencing large temperature differences between the atmosphere and the soil, which is relevant for soil chemical reactions.

Recently fixed carbon fuels microbial activity several meters below the soil surface

“…S1) caused by water limitation and low TOC content at this site. This is supported by in situ measurements of the soil CO2 concentration at the arid site at different soil depths that detected low CO2 concentrations throughout the year (Spohn and Holzheu, 2021).…”

“…The vegetation is sparse (10 % cover) and dominated by Proustia cuneifolia, Cordia decandra and Adesmia spp. (Spohn and Holzheu, 2021). The mediterranean site is located ~4.2 km south of the national park La Campana, in a water protection area.…”

Wind as a Driver of Peat CO2 Dynamics in a Northern Bog

“…However, intermittent non-diffusive transport processes could override molecular diffusion and create phase shifts in peat CO 2 emissions, with periods of storage and delayed emission relative to production. These non-diffusive transport processes can operate across multiple timescales and include convective fluxes, such as thermal convection (Spohn and Holzheu, 2021), pressure pumping (Massman 2006) and buoyancy flow (Rappoldt and others 2003), turbulent diffusion (Campeau and others 2021) and advective fluxes, such as soil venting (Hirsch and others 2004;Redeker and others 2015;Moya and others 2022). These processes may not considerably alter the estimate of the annual C balance of ecosystems, but nonetheless represent important underlying mechanisms that determine the magnitude and timing of soil CO 2 emission at a shorter timescale.…”

Short-Term Soil CO2 Concentration Responses to Precipitation Events in Karst Land with Diverse Vegetation Coverage in Southwestern China

“…However, most of previous studies focused on respiration in surface soils, which may neglect information at deeper depths . Recently, industrial solid-state sensors were developed to enable continuous and in situ monitoring of soil CO 2 profiles. ,, The development of new CO 2 sensor techniques has facilitated high-frequency measurements, making investigations into hourly and subhourly changes in soil CO 2 concentrations possible. , Rey et al highlighted the potential of these new technologies (including advanced automatic chambers, CO 2 concentration profiles, and isotope techniques) in providing further insights into the dynamics and sources of C in the soil.…”

“…14,15,25 The development of new CO 2 sensor techniques has facilitated high-frequency measurements, making investigations into hourly and subhourly changes in soil CO 2 concentrations possible. 26,27 Rey et al 28 highlighted the potential of these new technologies (including advanced automatic chambers, CO 2 concentration profiles, and isotope techniques) in providing further insights into the dynamics and sources of C in the soil.…”