ISOLAG

Contact
Nina Buchmann

Project members
Nina Buchmann
Romain Barnard
Yann Salmon

Related infrastructure
Phytotron
ISOLAB

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 (δ¹³C_R). 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: Kodama et al. 2008, Oecologia
• Oxygen isotopic signature was used to track the δ¹⁸O signal from leaf water to leaf and phloem organic matter: Barnard et al. 2007, PCE

More information

Funding: Swiss National Science Foundation

Timeframe: 2005-2008

Publications

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

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

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

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

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.

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 (accepted April 2011)