Effluxed CO2-13C from sterilized and unsterilized treatments of a calcareous soil

Soil inorganic carbon (C) represents a substantial C pool in and ecosystems, yet little data exist on the contribution of this pool to ecosystem C fluxes. A closed jar incubation study was carried out to test the hypothesis that CO2-C-13 production and response to sterilization would differ in a calcareous (Mojave Desert) soil and a non-calcareous (Oklahoma Prairie) soil due to contributions of carbonate-derived CO2. In addition to non-sterilized controls, soils were subjected to sterilization treatments (unbuffered HgCl2 addition for Oklahoma soil and unbuffered HgCl2 addition, buffered HgCl2 addition, and autoclaving for Mojave Desert soil) to decrease biotic respiration and more readily measure abiotic CO2 flux. Temperature and moisture treatments were also included with sterilization treatments in a factorial design. The rate of CO2 production in both soils was significantly decreased (36-87%) by sterilization, but sterilization treatments differed in effectiveness. Sterilization had no significant effect on effluxed CO2-C-13 values in the non-calcareous Oklahoma Prairie soil and autoclaved Mojave Desert soil as compared to their respective non-sterilized controls. However, sterilization significantly altered CO2-C-13 values in Mojave Desert soil HgCl2 sterilization treatments (both buffered and non-buffered). Plots of 1/CO2 versus CO2-delta C-13 (similar to Keeling plots) indicated that the source CO2-delta C-13 value of the Oklahoma Prairie soil treatments was similar to the delta C-13 value of soil organic matter [(SOM); -17.76 parts per thousand VPDB] whereas the source for the (acidic) unbuffered-HgCl2 sterilized Mojave Desert soil was similar to the delta C-13 value of carbonates (-0.93 parts per thousand VPDB). The source CO2-delta C-13 value of non-sterilized and autoclaved (-18.4 parts per thousand VPDB) Mojave Desert soil treatments was intermediate between SOM (-21.43 parts per thousand VPDB) and carbonates and indicates up to 13% of total C efflux may be from abiotic sources in calcareous soils. (c) 2006 Elsevier Ltd. All rights reserved.