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Updated: Jun 12, 2026

Utilizing Soil Density Fractionation to Separate Distinct Soil Carbon Pools
Published on: December 16, 2022
Diffusive fractionation complicates isotopic partitioning of autotrophic and heterotrophic sources of soil
Andrew B Moyes1, Sarah J Gaines, Rolf T W Siegwolf
1University of Utah, Department of Biology, 257 South, 1400 East, Salt Lake City, UT 84112, USA. amoyes@ucmerced.edu
Abstract:
Carbon isotope ratios (δ¹³C) of heterotrophic and rhizospheric sources of soil respiration under deciduous trees were evaluated over two growing seasons. Fluxes and δ¹³C of soil respiratory CO₂ on trenched and untrenched plots were calculated from closed chambers, profiles of soil CO₂ mole fraction and δ¹³C and continuous open chambers. δ¹³C of respired CO₂ and bulk carbon were measured from excised leaves and roots and sieved soil cores. Large diel variations (>5‰) in δ¹³C of soil respiration were observed when diel flux variability was large relative to average daily fluxes, independent of trenching. Soil gas transport modelling supported the conclusion that diel surface flux δ¹³C variation was driven by non-steady state gas transport effects. Active roots were associated with high summertime soil respiration rates and around 1‰ enrichment in the daily average δ¹³C of the soil surface CO₂ flux. Seasonal δ¹³C variability of about 4‰ (most enriched in summer) was observed on all plots and attributed to the heterotrophic CO₂ source.
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