Thermally driven CO 2 adsorption/desorption and its effect on soil respiration
In the authors' words
Soil respiration counterbalances global photosynthesis, yet several aspects of this process remain unexplained despite decades of research: (i) nighttime negative soil carbon flux in drylands and (ii) diurnal temperature-dependent hysteresis patterns. We propose that abiotic CO 2 adsorption-desorption in the soil is the cause or contributor to these phenomena. Laboratory isotherms were conducted on desert soil at various diurnal temperatures and CO 2 partial pressure levels. These results, combined with field data from the Mojave Desert, demonstrate that adsorption causes negative nocturnal CO 2 fluxes, while desorption during the day leads to positive fluxes. In addition, by accounting for thermally driven physical CO 2 exchange, the apparent temperature hysteresis commonly observed is reversed. The annual CO 2 adsorption in the thermally active soil layer ranges from 16.7 to 19.3 grams of CO 2 -C per square meter per year, indicating a possible abiotic exchange of up to 2.2 to 2.5 billion tonnes of CO 2 -C with the atmosphere globally. Our findings suggest that gaseous adsorption should be included in the global carbon cycle to more accurately represent land-atmosphere CO 2 exchange.
Appeared: Friday, September 25. Science Advances. Peer-reviewed journal.