Magnitude of the CO2 fertilization effect in tropical forests and boreal peatlands: Observations and modelling

Forests and peatlands dominate contemporary terrestrial carbon stocks and impact radiative forcing throughexchange with the atmosphere.

Rising temperatures and C O concentrations influence the exchange fluxes ofthese ecosystems, but proxy- and satellite data and modelling give conflicting results, with serious consequencesfor the accuracy of climate model predictions.

We pioneer novel stable isotope methodology – isotopomerabundances, which constitute the unique isotope information contained in each individual molecular position of ametabolite.

Isotopomers allow us to link atmospheric biophysical controls to enzyme responses in plants,providing a powerful way of disentangling temperature and C O physiological effects on ecosystem functioning,and constraining process representations in models designed to project the evolution of biosphere carbon stocksunder global change scenarios.In this interdisciplinary collaboration we will: 1) Use manipulation experiments to identify and calibrateisotopomer signals for a set of tropical tree species and for Northern hemisphere Sphagnum mosses, andcomparing species with and without ability for N-fixation. 2) For both plant groups quantify - over the pastcentury - the interaction between “C O fertilization", temperature rise and plant N status. 3) Use the obtaineddata to update leaf metabolic representations in a globally benchmarked ecosystem model, using it to analysehistorical biospheric C fluxes and C balance changes