Abstract
As the second largest carbon flux in terrestrial ecosystems, the soil CO2 flux is closely related to the atmospheric CO2 concentration. The soil CO2 flux is the sum of biotic respiration and abiotic geochemical CO2 exchange; however, little is known about abiotic CO2 fluxes in arid areas. To investigate the relative contribution of abiotic and biotic soil CO2 fluxes over a diurnal course, the abiotic CO2 flux was distinguished by autoclaving sterilization in both saline and alkaline soils at an arid site in northwestern China. The results demonstrated that: (1) Over the diurnal course, the abiotic CO2 was a significant component of the soil CO2 flux in both saline and alkaline soil, which accounted for more than 56% of the diurnal soil CO2 flux. (2) There was a dramatic difference in the temperature response between biotic and abiotic CO2 fluxes: the response curves of biotic respiration were exponential in the saline soil and quadratic in the alkaline soil, while the abiotic CO2 flux was linearly correlated with soil temperature. They were of similar magnitude but with opposite signs: resulting in almost neutral carbon emissions on daily average. (3) Due to this covering up effect of the abiotic CO2 flux, biotic respiration was severely underestimated (directly measured soil CO2 flux was only one-seventh of the biotic CO2 flux in saline soil, and even an order of magnitude lower in alkaline soil). In addition, the soil CO2 flux masked the temperature-inhibition of biotic respiration in the alkaline soil, and veiled the differences in soil biological respiration between the saline and alkaline soils. Hence, the soil CO2 flux may not be an ideal representative of soil respiration in arid soil. Our study calls for a reappraisal of the definition of the soil CO2 flux and its temperature dependence in arid or saline/alkaline land. Further investigations of abiotic CO2 fluxes are needed to improve our understanding of arid land responses to global warming and to assist in identifying the underlying abiotic mechanisms.
Highlights
As the second largest carbon flux in terrestrial ecosystems, the soil CO2 flux is closely related to the atmospheric CO2 concentration
(2) There was a dramatic difference in the temperature response between biotic and abiotic CO2 fluxes: the response curves of biotic respiration were exponential in the saline soil and quadratic in the alkaline soil, while the abiotic CO2 flux was linearly correlated with soil temperature
There were no significant differences in the soil properties between the control and sterilized soils for each soil type (p > 0.05), which means that the sterilizing process did not alter the soil properties
Summary
As the second largest carbon flux in terrestrial ecosystems, the soil CO2 flux is closely related to the atmospheric CO2 concentration. To investigate the relative contribution of abiotic and biotic soil CO2 fluxes over a diurnal course, the abiotic CO2 flux was distinguished by autoclaving sterilization in both saline and alkaline soils at an arid site in northwestern China. (2) There was a dramatic difference in the temperature response between biotic and abiotic CO2 fluxes: the response curves of biotic respiration were exponential in the saline soil and quadratic in the alkaline soil, while the abiotic CO2 flux was linearly correlated with soil temperature They were of similar magnitude but with opposite signs: resulting in almost neutral carbon emissions on daily average. Studies on the biotic and abiotic components of Fc in dry land soils are needed to better understand the feedback of the carbon cycle in response to climate change in arid areas. The basic hypothesis is that in dry land saline/alkaline soils, abiotic process contributes a significant portion in CO2 exchange between soil and atmosphere
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
