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

摘要

Soil inorganic carbon (C) represents a substantial C pool in arid 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 CO2-13C 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 CO2-13C 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 CO2-13C values in Mojave Desert soil HgCl2 sterilization treatments (both buffered and non-buffered). Plots of 1/CO2 versus CO2- delta 13C (similar to Keeling plots) indicated that the source CO2- delta 13C value of the Oklahoma Prairie soil treatments was similar to the delta 13C value of soil organic matter [(SOM); -17.76 per mil VPDB] whereas the source for the (acidic) unbuffered-HgCl2 sterilized Mojave Desert soil was similar to the delta 13C value of carbonates (-0.93 per mil VPDB). The source CO2- delta 13C value of non-sterilized and autoclaved (-18.4 per mil VPDB) Mojave Desert soil treatments was intermediate between SOM (-21.43 per mil VPDB) and carbonates and indicates up to 13% of total C efflux may be from abiotic sources in calcareous soils..