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Belowground carbon allocation in a temperate beech forest: new insight into carbon residence time using whole tree 13C labelling

Abstract : Belowground carbon allocation is an important component of forest carbon budget, affecting tree growth (competition between aboveground and belowground carbon sinks), acquisition of belowground resources (nutrients and water) that are often limiting forest ecosystems and soil carbon sequestration. Total belowground carbon flow can be estimated using a mass-balance approach as cumulative soil CO2 efflux minus the carbon input from aboveground litter plus the changes in the C stored in roots, in the forest floor, and in the soil, and further compared to gross annual production. While this approach is useful for understanding the whole ecosystem carbon budget, uncertainties remain about the contribution of the different belowground pools of carbon to ecosystem respiration and carbon sequestration. New insights into transfer rate and residence time of carbon in belowground compartments can be gained from in situ whole-crown 13C labelling experiments. We combined both approaches in a young temperate beech forest in north-eastern France where ecosystem carbon fluxes are recorded since a decade. Carbon allocated belowground represented less than 40% of gross primary production in this young beech forest. Autotrophic respiration assessed by comparing soil CO2 efflux measured on normal and on root exclusion plots, accounted for 60% of the total belowground carbon flow. This indicated a rather short mean residence time of carbon allocated belowground in the soil compartments. The recovery of 13C in soil CO2 efflux after pulse-labelling entire crowns of tree with 13CO2 at several occasions during the growing season was observed a few couple of hours after the labelling. That indicates a rapid transfer of 13C belowground with a maximum occurring within 2 to 4 days after labelling. Label was recovered at the same time in the respiration and in the biomass of both fine roots and soil microbes. Allocation of recently assimilated carbon to soil microbial respiration was greater in early summer compared to spring, late summer and autumn. A compartmental analysis indicated that the labelled substrate leaving the crown pool fills a metabolically active pool that contributes to soil CO2 efflux after a time lag, and from where it can be transferred and back transferred to a metabolically inactive pool, both pools being of similar size. Comparison with similar studies in other forest ecosystems indicates that the patterns of carbon allocation belowground are specie-specific and change seasonally according to the phenology of the species and to the climate.
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Conference papers
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https://hal.inrae.fr/hal-02804601
Contributor : Migration Prodinra <>
Submitted on : Friday, June 5, 2020 - 11:33:32 PM
Last modification on : Wednesday, February 24, 2021 - 3:30:53 AM

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  • HAL Id : hal-02804601, version 1
  • PRODINRA : 180834

Citation

Daniel Epron, Jérome Ngao, Caroline Plain, Bernard Longdoz, André Granier. Belowground carbon allocation in a temperate beech forest: new insight into carbon residence time using whole tree 13C labelling. AGU Fall Meeting, Dec 2011, San Francisco, United States. ⟨hal-02804601⟩

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