Rationale
Quantifying terrestrial carbon storage and predicting the sensitivity of ecosystems to climate change relies on our ability to obtain observational constraints on photosynthetic and respiratory activity at large scales (ecosystem, regional and global). Currently, large-scale estimates of photosynthesis and respiration are principally derived from models that use parameterisations of carbon-climate feedbacks that are based on highly uncertain climate sensitivities for photosynthesis and respiration. Here we present a multi-tracer approach to constrain our estimates of photosynthesis and respiration at large scales and better represent these processes in vegetation models.
In terrestrial ecosystems, dissolved CO2 in leaf and soil water pools rapidly goes into oxygen isotopic equilibrium with water [CO2+H218O⇔H2O+CO18O]. In leaves, where the enzyme carbonic anhydrase (CA) is present and abundant, this isotopic equilibrium is reached almost instantaneously. As a consequence, and because soil and leaf water pools have different oxygen isotope composition (δ18O), CO2 fluxes from leaves and soils carry very distinct δ18O signals and can thus be tracked from the fluctuations in the δ18O of atmospheric CO2.
Scheme illustrating why the 18O/16O ratio in atmospheric CO2 could be useful to track separately CO2 fluxes from soils and leaves over land.
Scheme illustrating why the atmospheric COS concentrations could be useful to track gross one-way CO2 fluxes from leaves over land.
Recent studies also suggest that carbonyl sulphide (COS) is a good tracer of CO2 transfer into foliage because COS molecules diffuse like CO2 molecules through stomataand also react with CA inside mesophyll cells. However while CO2 reversibly interacts with CA and can diffuse back to the atmosphere before reaching a carboxylation site, COS undergoes an irreversible hydrolysis to form hydrogen sulphide [COS+H2O→H2S+CO2]. Thus, given the heterogeneous distribution of CA in mesophyll cells, the exact relationship between leaf COS, CO18O and CO2 fluxes is still unclear. In addition, as CA is widespread in diverse species from the Archaea, Bacteria and Algae domains, rapid CO2-H2O isotopic exchange and COS hydrolysis may also occur at the soil surface. Soil CA activity was neglected in global CO18O budgets until studies led by the EcoFun team demonstrated the necessity to account for it in order to explain δ18O measurements of the net soil CO2 efflux. The EcoFun team also demonstrated that soil CA plays an extremely important role in the global CO18O mass balance and strongly affects the magnitude of global photosynthesis derived with this tracer. Understanding how CA activity is regulated in terrestrial ecosystems is the key for using atmospheric budgets of COS and the δ18O of CO2 to constraint the existing parameterisation of CO2 gas exchange embedded in current models and increase the accuracy of our large-scale estimates of photosynthesis and respiration over land.
Overall objective and long-term goal
The overall objective of the project is to produce the necessary process understanding and modelling of CA activity in terrestrial ecosystems in order to enable the scientific community working on the global carbon cycle to optimally use COS and the δ18O in atmospheric CO2 as additional tracers of global CO2 budgets, and to increase significantly the accuracy of our large-scale estimates of photosynthesis (GPP) and respiration over land (long-term goal).
Project organisation
The project is organised into four main work packages:
WP1: leaf-level processes
In this work package, our aim is to characterise the COS transport and CA activity within the leaf using gas exchange and isotopic tracing techniques on wild species but also mutants with different CA isoforms, in order to better understand how COS and CO2 fluxes are related at the leaf level and respond to environmental factors.
WP2: soil-level processes
In this work package, we want to characterise simultaneously COS and CO18O uptake by soil monoliths, the relative abundance and community structure of soil bacteria, fungi and algae and their response to controlled moisture and temperature variations in order to quantify precisely soil CA activity from different soil types and identify its main drivers.
WP3: integration at the ecosystem scale
For this work package, we explore how continuous flux measurements of COS and CO18O at the ecosystem and component scales can be used to constraint photosynthetic and respiratory processes in multi-tracer land surface models.
WP4: model integration, coordination and dissemination
Here we combine all the theoretical knowledge gained from the other work packages into a coherent modelling framework, compatible with global land surface models, in order to provide the theoretical basis for using COS and CO18O as additional tracers of the global CO2 budget.
Project partners
The project gathers 3 partners:
- UMR1391 ISPA (where the EcoFun team is) brings the necessary expertise in soil gas exchange and eddy-covariance measurements, ecophysiological modelling and isotope geochemistry
- UMR 7265 BVME brings the necessary expertise in plant physiology and biophysics
- UMR 1347 AgroEcologie brings the necessary expertise in soil microbial ecology and genetics
Publications and communications
Work carried out in the framework of the ORCA project has been showcased in nearly >15 scientific articles (all “open access” but one), a PhD thesis (in biogeochemistry and microbial ecology), nearly 40 oral or poster presentations (including 4 invited ones) and a declaration of invention (for the taxonomic affiliation of DNA sequences from phototrophic micro- organisms, with potential applications, such as the development of bio-indicators of soil quality).
Multi-partner peer-reviewed articles
Djemiel C., Plassard D., Crouzet O., Sauze J., Mondy S., Nowak V., Terrat S., Wingate L., Ogée J., Maron P.-A. (2019) μgreen-db: a reference database of the plastidial 23S rRNA gene of photosynthetic eukaryotic algae and cyanobacteria. Submitted to Molecular Ecology Ressources (December 2018).
Ogée J., Genty B. & Wingate L. (2018) Revisiting the role of carbonic anhydrase activity on the CO18O discrimination during leaf photosynthesis. Plant Physiology, 178, 728–752, doi:10.1104/pp.17.01031. 
Sauze J., Ogée J., Maron P.A., Crouzet O., Nowak V., Wohl S., Kaisermann A., Jones S. & Wingate L. (2017) The interaction of soil phototrophs and fungi with pH and their impact on soil CO2, CO18O and OCS exchange. Soil, Biology & Biochemistry, 115, 371-382, doi: 10.1016/j.soilbio.2017.09.009.
Gimeno T., Ogée J., Royles J., Gibon Y., West J.B., Burlett R., Jones S.P., Sauze J., Wohl S., Benard C., Genty B. & Wingate L. (2017) Bryophyte gas-exchange dynamics along varying hydration status reveal significant COS emission in the light. New Phytologist, 215, 965–976, doi10.1111/nph.14584.
Ogée J., Sauze J., Kesselmeier J., Genty B., Van Diest H., Launois T., Wingate L. (2016) A new mechanistic framework to predict OCS fluxes from soils. Biogeosciences, 13, 2221–2240, doi:10.5194/bg-13-2221-2016.
Single-partner peer-reviewed articles
Jones S.P., Kaisermann A., Ogée J., Wohl S., Cheesman A.W., Cernusak L.A., Lloyd J., Wingate L. (2019) Controls on the rate of oxygen isotope exchange between soil waters and carbon dioxide. To be submitted to Biogeosciences Discussion in January 2019.
Kaisermann A., Jones S.P., Wohl S., González Muñoz N., Ogée J., Wingate L. (2019) Plant species growth influences soil carbonyl sulfide fluxes. To be submitted to Soil systems in January 2019.
Barbeta A., Jones S.P., Clavé L., Wingate L., Gimeno T.E., Fréjaville B., Wohl S., Ogée J. (2018). Hydrogen isotope fractionation affects the identification and quantification of tree water sources in a riparian forest. Hydrology and Earth System Sciences Discussions, 1– 29, doi:10.5194/hess-2018-402-RC3.
Gimeno T.E., Saavedra N., Ogée J., Medlyn B.E., Wingate L. (in review) A novel optimization approach incorporating non-stomatal limitations predicts stomatal behaviour on six plant functional types. Journal of Experimental Botany.
Kaisermann A., Jones S.P., Wohl S., Ogée J., Wingate L. (2018a). Nitrogen fertilization reduces the capacity of soils to take up atmospheric carbonyl sulphide. Soil systems, 2(4), 62. doi:10.3390/soilsystems2040062.
Meredith L.K., Boye K., Youngerman C., Whelan M., Ogée J., Sauze J., Wingate L. (2018a) Coupled Biological and Abiotic Mechanisms Driving Carbonyl Sulfide Production in Soils. Soil systems, 2, 37, doi:10.1126/science.aap9516.
Meredith L.K., Ogée J., Boye K., Singer E., Wingate L., von Sperber C., Sengupta A., Whelan M., Pang E., Keiluweit M., Brüggemann N., Berry J.A., Welander P.V. (2018b) Soil exchange rates of COS and CO18O differ with the diversity of microbial communities and their carbonic anhydrase enzymes. The ISME Journal, doi: 10.1038/s41396-018-0270-2.
Whelan M., Lennartz S., Gimeno T., Wehr R., Wohlfahrt G., Wang Y., Kooijmans L., Hilton T., Belviso S., Peylin P., Commane R., Sun W., Chen H., Kuai L., Mammarella I., Maseyk K., Berkelhammer M., Li K-F., Yakir D., Zumkehr A., Katayama Y., Ogée J., Speilmann F., Kitz F., Rastogi B., Kesselmeier J., Marshall J., Erkkila K-M., Wingate L., Meredith L., He W., Bunk R., Launois T., Vesala T., Schmidt J., Fichot C., Seibt U., Saleska S., Saltzman E., Montzka S, Berry J. & Campbell J.E. (2017) Reviews and Syntheses: Carbonyl sulfide as a multi-scale tracer for carbon and water cycles. Biogeosciences, 15, 3625–3657, doi:10.5194/bg-15-3625-2018.
Sauze J., Jones S., Wingate L., Wohl S. & Ogée J. (2018) The role of soil pH on soil carbonic anhydrase activity. Biogeosciences, 15, 597–612, doi: 10.5194/bg-15-597-2018.
Jones S., Ogée J., Sauze J., Wohl S., Saavedra N., Fernandez-Prado N., Maire J., Launois T., Bosc A., & Wingate L. (2017) Non-destructive estimates of soil carbonic anhydrase activity and soil water oxygen isotope composition. Hydrology and Earth System Sciences, 21:6363-6377, doi: 10.5194/hess-21-6363-2017.
Belviso S., Reiter I.M., Loubet B., Gros V., Lathière J., Montagne D., Delmotte M., Ramonet M., Kalogridis C., Lebegue B., Bonnaire N., Kazan V., Gauquelin T., Fernandez C., Genty B. (2016) A top-down approach of surface carbonyl sulfide exchange by a Mediterranean oak forest ecosystem in Southern France. Atmos. Chem. Phys., 16, 14909– 14923. doi:10.5194/acp-16-14909-2016.
Gangi L., Rothfuss Y., Ogée J., Wingate L., Vereecken H., Brüggemann N. (2015) A new method for in situ measurements of delta-18O of soil water and CO2 with high time resolution. Vadose Zone Journal, 14(8), doi:10.2136/vzj2014.11.0169. 
MSc and PhD theses
Sauze J. (2017) Identification des moteurs de l’activité de l’anhydrase carbonique dans les sols et son impact sur les échanges sol-atmosphère de CO18O et OCS, deux traceurs complémentaires du cycle du carbone. Thèse de doctorat de l’université de Bordeaux, soutenue le 7 avril 2017. http://www.theses.fr/2017BORD0568.
Cochet Y. (2016) Disentangling the interconnected pathways of CO2 and water in leaves. Thèse de Master de l’université de Bordeaux, soutenue le 21 Juin 2016. Encadrant(s): Prof. J. West et T. Gimeno.
Patents and others
Déclaration d’invention INRA n°DI-RV-17-0038 « base de données de séquences 23S de l’ADN ribosomique plastidial pour identifier les microorganismes photosynthétiques dans les matrices environnementales : outil μgreen-database ». Adresse web d’hébergement : microgreen- 23sdatabase.ea.inra.fr.
Project meetings and reports
Minutes and presentation of the different project meetings, as well as project reports sent to the funding body (ANR) can be found here.
Final report of the project (in french) can be found here.