Susceptibility of soil organic carbon to priming after long-term CO2 fumigation is mediated by soil texture

Qiao Xu; Jian Jin; Xiaojuan Wang; Roger Armstrong; Caixian Tang

doi:10.1016/j.scitotenv.2018.11.437

Susceptibility of soil organic carbon to priming after long-term CO₂ fumigation is mediated by soil texture

Sci Total Environ. 2019 Mar 20:657:1112-1120. doi: 10.1016/j.scitotenv.2018.11.437. Epub 2018 Nov 29.

Authors

Qiao Xu¹, Jian Jin¹, Xiaojuan Wang¹, Roger Armstrong², Caixian Tang³

Affiliations

¹ Department of Animal, Plant and Soil Sciences, Centre for AgriBioscience, La Trobe University, Melbourne, VIC 3086, Australia.
² Department of Economic Development, Jobs, Transport and Resources, Horsham, VIC 3401, Australia.
³ Department of Animal, Plant and Soil Sciences, Centre for AgriBioscience, La Trobe University, Melbourne, VIC 3086, Australia. Electronic address: C.Tang@latrobe.edu.au.

PMID: 30677878
DOI: 10.1016/j.scitotenv.2018.11.437

Abstract

Elevated CO₂ (eCO₂) may enhance soil organic carbon (SOC) sequestration via greater input of photosynthetic carbon (C). However, greater rhizodeposits under eCO₂ may stimulate microbial decomposition of native SOC. This study aimed to examine the status and stability of SOC in three Australian cropping soils after long-term CO₂ enrichment. Samples (0-5 cm) of Chromosol, Vertosol and Calcarosol soils were collected from an 8-year Free-air CO₂ Enrichment (SoilFACE) experiment and were used to examine SOC dynamics by physical fractionation and incubation with ¹³C-glucose. Compared to the ambient CO₂ (aCO₂) (390-400 μmol mol^-1), 8 years of elevated CO₂ (eCO₂) (550 μmol mol^-1) did not increase SOC concentration of all soils, but changed SOC distribution with 12% more C in coarse soil fractions and 5% less C in fine fractions. Elevated CO₂ also enhanced the susceptibility of SOC to ¹³C-glucose-induced priming, but this effect was only significant in the coarse-textured Calcarosol topsoil. The eCO₂ history increased labile C (coarse C fraction, +13%) and soil pH (+0.25 units), and decreased available N (-30%) in the Calcarosol, which stimulated microbial biomass C by 28%, leading to an enhanced priming effect. Despite with greater total primed C, the Chromosol that had the highest amount of native C, had lower primed C per unit of SOC when compared to the low-C Calcarosol. In conclusion, the effect of long-term eCO₂ enrichment on soil C and N availability in cropping soils depended on soil type with the coarse-textured Calcarosol soil being more susceptible to substrate-induced decomposition of its SOC.

Keywords: (13)C-glucose; Free-air CO(2) enrichment (FACE); Physical fractionation; Priming effect; SOC stability.