Summer School "Ecology and Society: Frontiers and Boundaries" / 3 - 7 June 2019

Using stable isotopes to link ecosystem processes to the global cycling of water and CO2 - Lisa WINGATE

Quantifying terrestrial carbon storage and predicting the sensitivity of ecosystems to climate change relies on our ability to obtain observational constraints on photosynthesis and respiration at large scales (ecosystem, regional and global). Estimates of global GPP can be obtained from an atmospheric budget of the oxygen isotopic composition (?18O) of atmospheric CO2, provided that we have a good knowledge of the ?18O signatures of terrestrial CO2 fluxes. The latter reflect the ?18O of leaf and soil water pools because CO2 exchanges “isotopically” with water [CO2+H218O?H2O+CO18O]. This exchange can be accelerated by the enzyme carbonic anhydrase (CA). As soil and leaf water pools have different ?18O signatures, CO2 fluxes from leaves and soils carry very distinct ?18O signals and can thus be tracked from the fluctuations in the ?18O of atmospheric CO2 (?a). In this seminar I will present the current state of understanding of the environmental and ecological causes behind the variability in the ?18O signatures of terrestrial CO2 and water fluxes and illustrate how this variability can influence our estimates of global GPP inferred from ?a budgets.