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Biogeosciences Discuss., 8, 885-919, 2011
www.biogeosciences-discuss.net/8/885/2011/ doi:10.5194/bgd-8-885-2011 © Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 License. |
Seasonal variations of belowground carbon transfer assessed by in situ 13CO2 pulse labelling of trees
1Université Henri Poincaré, UMR 1137, 54500 Vandoeuvre-les-Nancy, France
2INRA, UMR 1137, 54280 Champenoux, France
3Université Paris-Sud, UMR 8079, Orsay, 75231 Paris, France
4CNRS, UMR 8079, 91190 Gif-sur-Yvette, France
5AgroParisTech, UMR 8079, 75231 Paris, France
6INRA, UR1263, 33140 Villenave d'Ornon, France
7Kyoto University, Laboratory of Forest Utilization, Kyoto 606-8502, Japan
8ENITA de Bordeaux, UMR 1220, 33883 Villenave d 'Ornon, France
9INRA, UMR 1220, 33883 Villenave d'Ornon, France
10INRA, UR 1138, Centre de Nancy, 54280 Champenoux, France
11UPMC-Paris6, UMR7618, 75230 Paris, France
Abstract. Soil CO2 efflux is the main source of CO2 from forest ecosystems and it is tightly coupled to the transfer of recent photosynthetic assimilates belowground and their metabolism in roots, mycorrhiza and rhizosphere microorganisms feeding on root-derived exudates. The objectives of our study were to assess patterns of belowground carbon allocation among tree species and along seasons. Pure 13CO2 pulse labelling of the entire crown of three different tree species (beech, oak and pine) was carried out at distinct phenological stages. Excess 13C in soil CO2 efflux was tracked using tunable diode laser absorption spectrometry to determine time lags between the start of the labelling and the appearance of 13C in soil CO2 efflux and the amount of 13C allocated to soil CO2 efflux. Isotope composition (δ13C) of CO2 respired by fine roots and soil microbes was measured at several occasions after labelling, together with δ13C of bulk root tissue and microbial carbon. Time lags ranged from 0.5 to 1.3 days in beech and oak and were longer in pine (1.6–2.7 days during the active growing season, more than 4 days during the resting season), and the transfer of C to the microbial biomass was as fast as to the fine roots. The amount of 13C allocated to soil CO2 efflux was estimated from a compartment model. Seasonal patterns of carbon allocation to soil CO2 efflux differed markedly between species, with pronounced seasonal variations in pine and beech. In beech, it may reflect competition with other sinks (aboveground growth in late spring and storage in late summer) that were not observed in oak.
Citation: Epron, D., Ngao, J., Dannoura, M., Bakker, M. R., Zeller, B., Bazot, S., Bosc, A., Plain, C., Lata, J. C., Priault, P., Barthes, L., and Loustau, D.: Seasonal variations of belowground carbon transfer assessed by in situ 13CO2 pulse labelling of trees, Biogeosciences Discuss., 8, 885-919, doi:10.5194/bgd-8-885-2011, 2011.