Reconciling change in Oi-horizon carbon-14 with mass loss for an oak forest

First-year litter decomposition was estimated for an upland-oak (Quercus spp.) forest ecosystem using enrichment or dilution of the 14C-signature of the Oi-horizon. These isotopically based mass-loss estimates were contrasted with measured mass-loss rates from past litterbag studies. Mass-loss deriv...

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Bibliographic Details
Published in:Soil Science Society of America journal 2005-09, Vol.69 (5), p.1492-1502
Main Authors: Hanson, P.J, Swanston, C.W, Garten, C.T. Jr, Todd, D.E, Trumbore, S.E
Format: Article
Language:English
Subjects:
Agronomy. Soil science and plant productions
Animal and plant ecology
Animal, plant and microbial ecology
biodegradation
biological activity in soil
Biological and medical sciences
CARBON
CARBON 14
Chemical, physicochemical, biochemical and biological properties
Climate change
CLIMATIC CHANGE
COMMINUTION
deciduous forests
DILUTION
Earth sciences
Earth, ocean, space
ECOSYSTEMS
ENVIRONMENTAL SCIENCES
Exact sciences and technology
forest litter
Forest soils
FORESTS
FRAGMENTATION
Fundamental and applied biological sciences. Psychology
Geochemistry
montane forests
OAKS
organic horizons
Organic matter
Physics, chemistry, biochemistry and biology of agricultural and forest soils
Quercus
radionuclides
RECYCLING
Soil and rock geochemistry
soil microorganisms
Soil science
Soil sciences
SOILS
Surficial geology
Synecology
Terrestrial ecosystems
TRANSPORT
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Summary:First-year litter decomposition was estimated for an upland-oak (Quercus spp.) forest ecosystem using enrichment or dilution of the 14C-signature of the Oi-horizon. These isotopically based mass-loss estimates were contrasted with measured mass-loss rates from past litterbag studies. Mass-loss derived from changes in the 14C-signature of the Oi-horizon suggested mean mass loss over 9 mo of 45%, which was higher than the corresponding 9-mo rate extrapolated from litterbag studies (approximately 35%). Greater mass loss was expected from the isotopic approach because litterbags are known to limit mass loss processes driven by soil macrofauna (e.g., fragmentation and comminution). Although the 14C-isotope approach offers the advantage of being a non-invasive method, it exhibited high variability that undermined its utility as an alternative to routine litterbag mass loss methods. However, the 14C approach measures the residence time of C in the leaf litter, rather than the time it takes for leaves to disappear; hence radiocarbon measures reflect C immobilization and recycling in the microbial pool, and do not necessarily replicate results from litterbag mass loss. The commonly applied two-compartment isotopic mixing model was appropriate for estimating decomposition from isotopic enrichment of near-background soils, but it produced divergent results for isotopic dilution of a multi-layered system with litter cohorts having independent 14C-signatures. This discrepancy suggests that cohort-based models are needed to adequately capture the complex processes involved in C transport associated with litter mass-loss. Such models will be crucial for predicting intra- and interannual differences in organic horizon decomposition driven by scenarios of climatic change.
ISSN:0361-5995
1435-0661
1435-0661
DOI:10.2136/sssaj2004.0300