Abiotic CO2 exchange between soil and atmosphere and its response to temperature

Abstract

Although abiotic CO 2 exchange between soil and atmosphere is often observed in deserts, its contribution to carbon balance and accurate response to soil temperature (T s (°C)) are still uncertain. Abiotic soil carbon flux (ASCF) and T s were continuously measured on sterilized soil at 2-day intervals in the Mu Us Desert, northwestern China from May to October in 2012. The results showed that negative ASCF (CO 2 absorption) occurred at night while positive ASCF (CO 2 emission) during the day. Net CO 2 sequestration during the 6 months totaled 64.37 g CO2 m -2 (0.09 lmol m -2 s -1 ). On the seasonal scale, ASCF was weakly correlated with T s (c = 0.15, p \ 0.01), but showed a strong positive correlation with the rate of change in T s (DT/Dt (°C h -1 )) (c = 0.82, p \ 0.01). On the diurnal scale, ASCF showed clear hysteresis loops with respect to T s , but DT/Dt explained more than 85 % of the diurnal variations in ASCF for different months. The results indicate that a non-trivial CO 2 exchange process between soil and atmosphere can induce carbon sequestration and this exchange process is modified by temperature. Although soil temperature cannot be directly used to explain the effect of temperature on the abiotic soil carbon flux, the rate of change in soil temperature can accurately interpret the role of temperature played in the abiotic CO 2 exchange between soil and atmosphere. CO 2 absorption and emission by the desert soil is driven by the rate of falling and rising of T s , respectively. The findings may have significant implications for the global carbon cycle and may facilitate to explore the formation of this abiotic CO 2 exchange process.

Soil carbon dioxide emissions from the Mojave desert: Isotopic evidence for a carbonate source

“…The data presented here add an independent line of isotopic verification to the growing body of evidence that abiotic processes are important element of the C cycle in desert soils. We show that diurnally evolved CO 2 arises in part from carbonate sources, providing a source to balance the nighttime CO 2 uptake observed in arid systems [ Hamerlynck et al ., ; Liu et al ., ; Yates et al ., ; Xie et al ., ] and likely keeping the system at (or close to) a state of C equilibrium [ Schlesinger , ].…”

“…One line of evidence for an abiotic C flux comes from eddy covariance and chamber methods [ Xie et al ., ; Yates et al ., ; Hamerlynck et al ., ; Ma et al ., ], indicating that several arid ecosystems appear to take up CO 2 at night and exhibit positive fluxes from dry soils during the day. These observations are supported by lab experiments showing uptake, and some subsequent release, of isotopically labeled CO 2 [ Liu et al ., ; Fa et al ., ], as well as diel changes in CO 2 concentration [ Yates et al ., ; Liu et al ., ; Fa et al ., ].…”

Soil CO2 Uptake in Deserts and Its Implications to the Groundwater Environment

“…Although soil CO2 uptake in deserts has been investigated in many previous studies, its potential influences on the groundwater environment remain unaddressed [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. This is partially due to the lack of a simple method for the separation and quantification of such CO2 uptake.…”

“…Most studies assumed that these absorbed CO2 are partially dissolved in the soil-groundwater system. However, the magnitude of the beneath CO2 dissolution remains undetermined [25][26][27][28][29][30].…”

“…It has been widely recognized that the overall magnitude of CO2 dissolution beneath deserts and its contributions to the ecosystem carbon balance can be huge [30][31][32][33][34][35][36][37][38][39], but its effect on the local environment are seldom reported. As a first attempt to analyze the implications of the soil CO2 uptake to the groundwater environment, the present study simply assumes that the absorbed CO2 has been largely dissolved in the soil-groundwater system beneath the deserts.…”