Ecophysiological modeling of the climate imprint on photosynthesis and carbon allocation to the tree stem in the North American boreal forest

International audienceA better understanding of the coupling between photosynthesis and carbon allocation in the boreal forest, with implicated environmental factors and mechanistic rules, is crucial to accurately predict boreal forest carbon stocks and fluxes, which are significant components of the global carbon budget. Here we adapted the MAIDEN ecophysiological forest model to better consider important processes for boreal tree species, such as non-linear acclimation of photosynthesis to 15 temperature changes, canopy development as a function of previous year climate variables influencing bud formation, and temperature dependence of carbon partition in summer. We tested these modifications in the eastern Canadian taiga using black spruce (Picea mariana (Mill.) B.S.P.) gross primary production and ring-width data. MAIDEN explains 90% of the observed daily gross primary production variability, 73% of the full spectrum of the annual ring width variability and 20-30% of its high frequency component. The positive effect on stem growth due to climate warming in the last decades is well 20 captured by the model. In addition, we illustrate the improvement achieved with each introduced model adaptation and compare the model results with those of linear response functions. This shows that MAIDEN simulates robust relationships with the most important climate variables (those detected by classical response-function analysis), and is a powerful tool for understanding how environmental factors interact with black spruce ecophysiology to influence present-day and future boreal forest carbon fluxes. 2