title: Diffusive fractionation complicates isotopic partitioning of autotrophic and heterotrophic sources of soil respiration.
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.
authors.affiliation: University of Utah, Department of Biology, 257 South, 1400 East, Salt Lake City, UT 84112, USA. amoyes@ucmerced.edu
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Moyes
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Gaines
authors.forename: Rolf T W
authors.initials: RT
authors.lastname: Siegwolf
authors.forename: David R
authors.initials: DR
authors.lastname: Bowling
mesh_terms: D002245:Carbon Dioxide / Q000032:analysis*; D002247:Carbon Isotopes / Q000032:analysis; D008954:Models, Biological; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D058441:Rhizosphere; D012621:Seasons; D012987:Soil / Q000737:chemistry*; D013696:Temperature; D014197:Trees / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D012987:Soil; D002245:Carbon Dioxide