Biotic and Abiotic Responses of Soil CO2 Efflux to Short-term Rain Events in a Mojave Desert Ecosystem

Several studies show rapid responses of soil CO2 efflux to infrequent precipitation events in arid ecosystems but the processes causing these rapid responses are not always clear. We measured soil CO2 efflux following irrigation events at the Mojave Global Change Facility near Las Vegas, NV. We measured total soil CO2 efflux and isotopic composition of the CO2 under shrubs and in canopy interspaces. We used the Keeling approach to calculate the sources of the CO2. The CO2 efflux measurements showed that pulse responses were larger under shrubs than in canopy interspaces. The isotopic data showed that the source of CO2 was biogenic and we did not find evidence for the contribution of carbonates to the soil CO2 efflux. Soil CO2 concentrations down to 50 cm in the soil increased following the irrigation even though the water infiltration was much more shallow. This increase in soil CO2 concentrations may have been caused by temporarily clogging of soil pores by water preventing release of CO2 present deeper in the soil. Our results show that pulse responses in soil CO2 efflux following precipitation events are caused by shallow, most likely microbial responses and that soil air displacement is negligible.