ISOLAG
Biological and environmental controls of the isotopic time lag between assimilation and respiration
The aim of this project is to better understand the isotopic signatures along the atmosphere-assimilates-organic matter-respiration chain, focusing on the physiological links and controls of the isotopic time lag between assimilation and respiration.
Context
Current changes in global climate and land use/land cover require a profound understanding of the CO2 exchange of terrestrial ecosystems with the atmosphere. Field results from isotopic signatures of ecosystem CO2 exchange (isofluxes) showed a time lag of 4 to 10 days between carbon assimilation and belowground ecosystem respiration. So far the only example of direct control of isotopic time lags in ecosystem physiology has been atmospheric vapour pressure deficit (vpd) affecting the isotopic signature of ecosystem respiration (δ13CR). A mechanistic approach under controlled conditions is now needed to understand the biological and environmental controls of this time lag.
Objectives
Determination of the natural variability of the isotopic C signatures
of organic materials and respired CO2 along the atmosphere–assimilates–organic matter–respiration chain
- Effect of plant phenology
- Focus on soil functioning
Identification of the time lag length and ‰ shift between assimilation and respiration
Measured by the time between changes in environmental factors affecting leaf photosynthesis and changes in the isotopic signatures of plant- and soil-respired CO2
- Non-stressed conditions
- Vpd-stressed conditions
Effect of environmental and biological factors on the time lag
Approaches
Stand-alone experiments in plant growth chambers
- Controlled environment facility: Phytotron
- Plant species: herbs, grasses, tree saplings
- Natural abundance and 13C labelling
- Response at different time scales, from 24 hours to several months
δ13C measurements in the Isolab facility
- Bulk samples: plant leaf, stem, roots
- δ13C of CO2 respired by leaf, plant and soil determined by online IRMS measurement (Keeling plot)
- Assimilates: phloem collection by exudation method
Additional field approaches
- The ISOLAG question was explored under natural conditions in a pine forest, in collaboration with the Albert-Ludwig University of Freiburg: external pageKodama et al. 2008, Oecologiacall_made
- Oxygen isotopic signature was used to track the δ18O signal from leaf water to leaf and phloem organic matter: external pageBarnard et al. 2007, PCEcall_made
Publications
2016
Salmon Y, Buchmann N, Barnard RL (2016) Effects of ontogeny on δ13C of plant- and soil-respired CO2 and on respiratory carbon fractionation in C3 herbaceous species. PLoS ONE 11(3): e0151583. external pagedoi:10.1371/journal.pone.0151583call_made
2014
Salmon Y, Barnard R, Buchmann N (2014) Stomatal conductance mediates the isotopic time lag between leaf assimilation and soil CO2 efflux. Functional Plant Biology 41: 850-859 doi:10.1071/FP13212
2011
Brüggemann N, Gessler A, Kayler Z, Keel SG, Badeck F, Barthel M, Boeckx P, Buchmann N, Brugnoli E, Esperschütz J, Gavrichkova O, Ghashghaie J, Gomez-Casanovas N, Keitel C, Knohl A, Kuptz D, Palacio S, Salmon Y, Uchida Y, Bahn M (2011) Carbon allocation and carbon isotope fluxes in the plant–soil–atmosphere continuum: a review. Biogeosciences Discussion 8: 3619–3695
Salmon Y, Barnard R, Buchmann N (2011) Ontogeny and leaf gas exchange mediate the carbon isotopic signature of herbaceous plants. Plant, Cell and Environment 34: 465-479
Salmon Y, Buchmann N, Barnard R (2011) Response of δ13C in plant and soil respiration to a water pulse. Biogeosciences Discussion 8: 4493-4527
2009
Gessler A, Brandes E, Buchmann N, Helle G, Rennenberg H, Barnard RL (2009) Tracing carbon and oxygen isotope signals from newly assimilated sugars in the leaves to the tree ring archive. Plant, Cell and Environment 32:780-795
Richter A, Wanek W, Werner RA, Ghashghaie J, Jäggi M, Gessler A, Brugnoli E, Hettmann E, Göttlicher SG, Salmon Y, Bathellier C, Kodama N, Nogués S, Søe A, Volders F, Sörgel K, Blöchl A, Siegwolf RTW, Buchmann N, Gleixner G (2009) Preparation of starch and soluble sugars of plant material for analysis of carbon isotope composition: a comparison of methods. Rapid Communications in Mass Spectrometry 23: 2476–2488
2008
Kodama N, Barnard RL, Salmon Y, Weston C, Ferrio JP, Holst J, Werner RA, Saurer M, Rennenberg H, Buchmann N, Gessler A (2008) Temporal dynamics of the carbon isotope composition in a Pinus sylvestris stand – from newly assimilated organic carbon to respired carbon dioxide. Oecologia 156:737-750
2007
Barnard RL, Salmon Y, Kodama N, Sörgel K, Holst J, Rennenberg H, Gessler A, Buchmann N (2007) Evaporative enrichment and time-lags between δ18O of leaf water and organic pools in a pine stand. Plant, Cell and Environment 30:39-550