Detecting forest metabolic shifts over the past century: implications for the land carbon sink

Forests contribute strongly to terrestrial carbon (C) stocks and impact radiative forcing by C exchange with the atmosphere.

Efforts to constrain forests’ responses to interacting CO2 and temperature rises remain uncertain, with serious consequences for the accuracy of climate model predictions.

We pioneer novel stable isotope methodology – isotopomer abundances, which constitute the unique isotope information contained in each individual molecular position of a metabolite.

Isotopomers allow us to link atmospheric biophysical controls to enzyme responses in plants, providing a powerful way of disentangling temperature and CO2 physiological effects on ecosystem functioning, and constraining process representations in models designed to project the evolution of biosphere C stocks under global change scenarios.

In this interdisciplinary collaboration we will: 1) Use manipulation experiments to define isotopomer signals, in particular a signal tracking photorespiration. 2) Quantify - over the past century - interactions between “CO2 fertilization” and temperature rise; comparing coniferous and broadleaved species important for forestry and for C fluxes, to detect possible inter-species response variation. 3) Use the results to update leaf metabolic representations in a globally benchmarked ecosystem model, enabling analysis of historical- and prediction of future biospheric C fluxes.

The results will improve planning in forestry and the accuracy of Swedish C balance reporting.