Biotic and Abiotic Factors Controlling Soil Respiration Partitioning in a Tall Grass Prairie

Soil respiration is a major component of ecosystem respiration, and small changes in soil CO2 efflux can have a major impact on the amount of carbon released back to the atmosphere. Contributions to soil respiration come both from free-living soil microorganisms decomposing soil organic matter (heterotrophic respiration) and from roots and rhizosphere microorganisms (autotrophic respiration). Little is known about the factors underlying the partitioning of soil respiration into auto- and heterotrophic components, although increasing evidence shows that these components respond differently to vegetation, climate and environmental factors. We investigated biotic and abiotic factors that affect auto- and heterotrophic respiration in a 19-year-old restored tall grass prairie at Fermi National Accelerator Laboratory in Batavia, IL. Four automated soil respiration chambers continuously measured soil CO2 efflux during the growing season. Total soil respiration was separated into its hetero- and autotrophic components by using a stable- isotope mass balance technique based on the differential 13C/12C ratio of the respired CO2 from roots and soil at the site. Keeling plot measurements and root and soil incubations were conducted every three weeks at midday and at night to detect temporal changes in the end members that affect mass balance calculations during the growing season. Continuous measurements were also made of soil moisture, soil temperature, and net ecosystem exchange derived from eddy correlation techniques. Preliminary results show that regardless of diurnal variation, the proportion of autotrophic respiration to total respiration was larger during the earlier part of the growing season while the proportion of nighttime heterotrophic respiration to total respiration increased later in the growing season. Our results suggest that differential controlling factors for soil respiration components might be operating differently in time.