Biotic and Abiotic Contribution to Diurnal Soil CO2 Fluxes from Saline/Alkaline Soils

Abstract

As the second largest carbon flux in terrestrial ecosystems, the soil CO 2 flux is closely related to the atmospheric co 2 concentration. the soil co 2 flux is the sum of biotic respiration and abiotic geochemical co 2 exchange; however, little is known about abiotic co 2 fluxes in arid areas. To investigate the relative contribution of abiotic and biotic soil co 2 fluxes over a diurnal course, the abiotic CO 2 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 CO 2 was a significant component of the soil co 2 flux in both saline and alkaline soil, which accounted for more than 56% of the diurnal soil co 2 flux. (2) There was a dramatic difference in the temperature response between biotic and abiotic co 2 fluxes: the response curves of biotic respiration were exponential in the saline soil and quadratic in the alkaline soil, while the abiotic co 2 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 CO 2 flux, biotic respiration was severely underestimated (directly measured soil CO 2 flux was only one-seventh of the biotic CO 2 flux in saline soil, and even an order of magnitude lower in alkaline soil). In addition, the soil CO 2 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 co 2 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 co 2 flux and its temperature dependence in arid or saline/alkaline land. Further investigations of abiotic co 2 fluxes are needed to improve our understanding of arid land responses to global warming and to assist in identifying the underlying abiotic mechanisms.

Rhizosphere Effects of Maize and Wheat Increase Soil Organic and Inorganic Carbon Release in Carbonate-Rich Soils: A Three-Source 13C Partitioning Study

“…To determine the fractionation of SIC-derived CO 2 relative to SIC, it is important to eliminate the interference of SOC-derived CO 2 (Skidmore et al, 2004). Recently, a series of sterilization studies were conducted to partition the contribution of SIC to total soil CO 2 emissions by eliminating the microbial respiration process (Ma et al, 2017;Wang et al, 2020). Consequently, in future studies, isotope fractionation in δ 13 C values between SIC-and SIC-derived CO 2 should be measured by sterilization treatment.…”

“…In carbonate-rich soils, recent studies have found that soil-derived CO 2 emissions come not only from SOC decomposition but also from SIC dissolution. The contribution of SIC dissolution to soil C (SIC + SOC) release ranged from 3 to 95% in carbonate-rich soils without plants (Lardner et al, 2015;Schindlbacher et al, 2015;Wang et al, 2020). Therefore, SIC dissolution is more important to stabilize the global C pool and regulate atmospheric CO 2 concentrations than previously thought (Zamanian and Kuzyakov, 2019;Raza et al, 2020).…”

Wetting‐induced soil CO2 emission pulses are driven by interactions among soil temperature, carbon, and nitrogen limitation in the Colorado Desert

“…Maximum emissions of CO 2 from soils may occur during transient periods when multiple limiting resources become available to microorganisms (Choi et al, 2022;Seastedt & Knapp, 1993), suggesting that a combination of warmer and substrate-rich conditions could magnify soil CO 2 emission pulses. However, models of CO 2 emissions do not typically surpass 35°C (Davidson et al, 2012;Tian et al, 2015) and desert field studies show inconsistent soil respiration responses to higher temperatures, with some observing continued increases (Richardson et al, 2012;Zhang et al, 2010Zhang et al, , 2015 and others observing decreases (Leon et al, 2014;Wang et al, 2020) in CO 2 efflux at temperatures above 30°C. Simultaneously, soil CO 2 production generally increases with soil C concentrations (Eberwein et al, 2015;Evans et al, 2016), but this correlation may mask other factors that contribute to soil respiration such as root-microbe interactions (Ryan & Law, 2005) and soil stoichiometry (Choi et al, 2022;Liang et al, 2015).…”

CO2 emission affected by moisture content and aggregate sizes in a calcareous soil of Comarca Lagunera, Mexico

“…Soil CO 2 emissions comprise both biotic respiration related to SOC, and abiotic geochemical CO 2 exchange related to SIC (Wang et al, 2020). Incubation in a closed system is a common technique to measure CO 2 emission from soil (Pumpanen et al, 2000).…”