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See detailCarbon isotopic signature of CO2 emitted by plant compartments and soil in two temperate deciduous forests
Maunoury-Danger, F.; Chemidlin Prevost Boure, N.; Ngao, J. et al

in Annals of Forest Science (2013), 70(2), 173-183

• Context: 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 ... [more ▼]

• Context: 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. • Aims: We aimed to characterise simultaneously the seasonal dynamics of δ13CE in different compartments of two temperate broadleaved forest ecosystems. • Methods: 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. • Results: 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 δ 13CE and δ13C of organic matter. Causes for these seasonal variations and the vertical zonation in isotope signature are discussed. • Conclusion: 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. © 2012 INRA and Springer-Verlag France. [less ▲]

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See detailGround-based Network of NDVI measurements for tracking temporal dynamics of canopy structure and vegetation phenology in different biomes
Soudani, K.; Hmimina, K.; Delpierre, N. et al

in Remote Sensing of Environment (2012), 123

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See detailRoot exclusion through trenching does not affect the isotopic composition of soil CO2 efflux
Chemidlin Prevost-Boure, N.; Ngao, J.; Berveiller, D. et al

in Plant and Soil (2009), 319(1-2), 1-13

Disentangling the autotrophic and heterotrophic components of soil CO 2 efflux is critical to understanding the role of soil system in terrestrial carbon (C) cycling. In this study, we combined a stable C ... [more ▼]

Disentangling the autotrophic and heterotrophic components of soil CO 2 efflux is critical to understanding the role of soil system in terrestrial carbon (C) cycling. In this study, we combined a stable C-isotope natural abundance approach with the trenched plot method to determine if root exclusion significantly affected the isotopic composition (δ 13C) of soil CO2 efflux (RS). This study was performed in different forest ecosystems: a tropical rainforest and two temperate broadleaved forests, where trenched plots had previously been installed. At each site, RS and its δ13C (δ13CRs) tended to be lower in trenched plots than in control plots. Contrary to RS, δ13CRs differences were not significant. This observation is consistent with the small differences in δ13C measured on organic matter from root, litter and soil. The lack of an effect on δ13CRs by root exclusion could be from the small difference in δ13C between autotrophic and heterotrophic soil respirations, but further investigations are needed because of potential artefacts associated with the root exclusion technique. © 2008 Springer Science+Business Media B.V. [less ▲]

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See detailExceptional Carbon Uptake In European Forests During The Warm Spring Of 2007: A Data-Model Analysis
Delpierre, N.; Soudani, K.; Kostner, B. et al

in Global Change Biology (2009), 15(6), 1455-1474

Temperate and boreal forests undergo drastic functional changes in the springtime, shifting within a few weeks from net carbon (C) sources to net C sinks. Most of these changes are mediated by temperature ... [more ▼]

Temperate and boreal forests undergo drastic functional changes in the springtime, shifting within a few weeks from net carbon (C) sources to net C sinks. Most of these changes are mediated by temperature. The autumn 2006-winter 2007 record warm period was followed by an exceptionally warm spring in Europe, making spring 2007 a good candidate for advances in the onset of the photosynthetically active period. An analysis of a decade of eddy covariance data from six European forests stands, which encompass a wide range of functional types (broadleaf evergreen, broadleaf deciduous, needleleaf evergreen) and a wide latitudinal band (from 44 degrees to 62 degrees N), revealed exceptional fluxes during spring 2007. Gross primary productivity (GPP) of spring 2007 was the maximum recorded in the decade examined for all sites but a Mediterranean evergreen forest (with a +40 to +130 gC m(-2) anomaly compared with the decadal mean over the January-May period). Total ecosystem respiration (TER) was also promoted during spring 2007, though less anomalous than GPP (with a +17 to +93 gC m(-2) anomaly over 5 months), leading to higher net uptake than the long-term mean at all sites (+12 to +79 gC m(-2) anomaly over 5 months). A correlative analysis relating springtime C fluxes to simple phenological indices suggested spring C uptake and temperatures to be related. The CASTANEA process-based model was used to disentangle the seasonality of climatic drivers (incoming radiation, air and soil temperatures) and biological drivers (canopy dynamics, thermal acclimation of photosynthesis to low temperatures) on spring C fluxes along the latitudinal gradient. A sensitivity analysis of model simulations evidenced the roles of (i) an exceptional early budburst combined with elevated air temperature in deciduous sites, and (ii) an early relief of winter thermal acclimation in coniferous sites for the promotion of 2007 spring assimilation. [less ▲]

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