Informing climate models with rapid chamber measurements of forest carbon uptake

Abstract

Models predicting ecosystem carbon dioxide ( CO 2 ) exchange under future climate change rely on relatively few real‐world tests of their assumptions and outputs. Here, we demonstrate a rapid and cost‐effective method to estimate CO 2 exchange from intact vegetation patches under varying atmospheric CO 2 concentrations . We find that net ecosystem CO 2 uptake ( NEE ) in a boreal forest rose linearly by 4.7 ± 0.2% of the current ambient rate for every 10 ppm CO 2 increase, with no detectable influence of foliar biomass, season, or nitrogen (N) fertilization. The lack of any clear short‐term NEE response to fertilization in such an N‐limited system is inconsistent with the instantaneous downregulation of photosynthesis formalized in many global models. Incorporating an alternative mechanism with considerable empirical support – diversion of excess carbon to storage compounds – into an existing earth system model brings the model output into closer agreement with our field measurements. A global simulation incorporating this modified model reduces a long‐standing mismatch between the modeled and observed seasonal amplitude of atmospheric CO 2 . Wider application of this chamber approach would provide critical data needed to further improve modeled projections of biosphere–atmosphere CO 2 exchange in a changing climate.

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