Carbon isotopic signature of CO2 emitted by plant compartments and soil in two temperate deciduous forests
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The carbon isotope composition of the CO2 efflux (δ13CE) from ecosystem components is widely used to investigate carbon cycles and budgets at different ecosystem scales. δ13CE, was considered constant but is now known to vary along seasons. The seasonal variations have rarely been compared among different ecosystem components.
We aimed to characterise simultaneously the seasonal dynamics of δ13CE in different compartments of two temperate broadleaved forest ecosystems.
Using manual chambers and isotope ratio mass spectrometry, we recorded simultaneously δ13CE and δ13C of organic matter in sun leaves, current-year twigs, trunk bases and soil in an oak and a beech forest during 1 year.
In the two forests, δ13CE displayed a larger variability in the tree components than in the soil. During the leafy period, a pronounced vertical zonation of δ13CE was observed between the top (sun leaves and twigs with higher values) and bottom (trunk and soil with lower values) of the ecosystem. No correlation was found between δ13CE and δ13C of organic matter. Causes for these seasonal variations and the vertical zonation in isotope signature are discussed.
Our study shows clear differences in values as well as seasonal dynamics of δ13CE among different components in the two ecosystems. The temporal and local variation of δ13CE cannot be inferred from organic matter signature or CO2 emission rates.
KeywordsCarbon isotopic composition CO2 efflux Oak forest Beech forest
Trunk CO2 efflux
Soil CO2 efflux
Ecosystem CO2 efflux
Carbon isotope composition
Carbon isotope composition of CO2 efflux
δ13CE of ecosystem
δ13CE of leaves
δ13CE of twigs
δ13CE of trunk
δ13CE of soil
δ13C of total organic matter
δ13COM of leaf
δ13COM of twig
δ13COM of trunk
δ13C of soil total organic matter
Day of year
The authors are grateful to the Office National des Forêts, especially M. Bénard, for facilitating experimental work at Barbeau. We acknowledge N. Bréda (INRA Nancy, France) for trunk growth measurements at Hesse. The platform Métabolisme-Métabolome of the IFR87 is acknowledged for the isotope measurements. We are grateful to M. Danger and X. Raynaud for valuable discussions on the manuscript and to E. M. Gross for revising the manuscript. We thank two anonymous reviewers and the editor for their helpful comments and improvements to the manuscript.
This research was funded by the French projects ‘Ministère délégué à la recherche-ACI Jeunes Chercheurs’ (no. JC10009) and ‘Programme National ACI/FNS ECCO, PNBC’ (convention no. 0429 FNS) and by the ESE laboratory thanks to funds from Paris-Sud University and CNRS.
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