Partitioning sources of soil-respired CO2 and their seasonal variation using a unique radiocarbon tracer
- University of California, Irvine
- ORNL
Soil respiration is derived from heterotrophic (decomposition of soil organic matter) and autotrophic (root/rhizosphere respiration) sources, but there is considerable uncertainty about what factors control variations in their relative contributions in space and time. We took advantage of a unique whole-ecosystem radiocarbon label in a temperate forest to partition soil respiration into three sources: (1) recently photosynthesized carbon (C), which dominates root and rhizosphere respiration; (2) leaf litter decomposition and (3) decomposition of root litter and soil organic matter 41-2 years old. Heterotrophic sources and specifically leaf litter decomposition were large contributors to total soil respiration during the growing season. Relative contributions from leaf litter decomposition ranged from a low of 1 3% of total soil respiration (63 mgCm 2 h 1) when leaf litter was extremely dry, to a high of 42 16% (96 38mgCm 2 h 1). Total soil respiration fluxes varied with the strength of the leaf litter decomposition source, indicating that moisture-dependent changes in litter decomposition drive variability in total soil respiration fluxes. In the surface mineral soil layer, decomposition of C fixed in the original labeling event (3-5 years earlier) dominated the isotopic signature of heterotrophic respiration. Root/rhizosphere respiration accounted for 16 10% to 64 22% of total soil respiration, with highest relative contributions coinciding with low overall soil respiration fluxes. In contrast to leaf litter decomposition, root respiration fluxes did not exhibit marked temporal variation ranging from 34 14 to 40 16mgCm 2 h 1 at different times in the growing season with a single exception (88 35 mgCm 2 h 1). Radiocarbon signatures of root respired CO2 changed markedly between early and late spring (March vs. May), suggesting a switch from stored nonstructural carbohydrate sources to more recent photosynthetic products.
- Research Organization:
- Oak Ridge National Laboratory (ORNL); Oak Ridge National Environmental Research Park
- Sponsoring Organization:
- SC USDOE - Office of Science (SC)
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 930811
- Journal Information:
- Global Change Biology, Journal Name: Global Change Biology Vol. 12; ISSN GCBIFE; ISSN 1354-1013
- Country of Publication:
- United States
- Language:
- English
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