Dual-chamber measurements of δ13C of soil-respired CO2 partitioned using a field-based three end-member model

F. Albanito, J. L. McAllister, A Cescatti, P. Smith, D. Robinson

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

The contribution of old soil C (SOM) to total soil respiration (R-S) in forest has been a crucial topic in global change research, but remains uncertain. Isotopic methods, such as natural variations in carbon isotope composition (delta C-13) of soil respiration, are more frequently being applied, and show promise in separating heterotrophic and autotrophic contributions to R-S. However, natural and artificial modification of delta C-13(RS) can cause isotopic disequilibria in the soil-atmosphere system generating a mismatch between what is usually measured and what process-based models will predict. Here we report the partitioning of the soil surface CO2 flux in a warm Mediterranean forest into components derived from root, litter/humus, and SOM sources using a new, three end-member mixing model, and compare this with the conventional partitioning into autotrophic and heterotrophic components. The three end-member mixing model takes into account both the discrimination during CO2 respiration/decomposition of the three components, as well as the fractions of their CO2 fluxes integrated over the total soil profile mass. In addition, we used a novel dual-chamber technique to ensure that delta C-13(Rs) was subjected to minimal artefacts during measurement. We observed that by using measured soil surface CO2 concentrations as a baseline level for the dual-chamber operation, it was possible to achieve and monitor the necessary conservation of the soil CO2 steady-state diffusion conditions during the measurements, without using permanent collars inserted deeply into the soil. When R-s (8.64 g CO2 m(2) d(-1)) was partitioned into two components, the mean autotrophic and heterotrophic respiration was 56 and 44%, respectively. When Rs was partitioned using the three-way model, however, roots, litter/humus, and SOM contributed 30, 33, and 37% of the total flux. Our results confirm that to improve the estimates of the partitioning method, it is important to distinguish the fractional contribution of the long-term SOM-derived flux from younger and more labile sources. (C) 2011 Elsevier Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)106-115
Number of pages10
JournalSoil Biology and Biochemistry
Volume47
Issue number-
Early online date28 Dec 2011
DOIs
Publication statusPublished - Apr 2012

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Keywords

  • soil respiration
  • soil chamber
  • stable isotope
  • mixing model
  • soil organic matter
  • isotopic composition
  • carbon-dioxide
  • forest soil
  • organic-matter
  • litter decomposition
  • numerical evaluation
  • natural-abundance
  • gas-exchange
  • steady-state
  • elevated CO2

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