Multi-proxy analysis confirms the tight coupling of carbon assimilation and allocation, with divergent NSCs strategies in two boreal forest species

Understanding the link between photosynthesis and carbon allocation to woody biomass remains a critical gap in predicting forest responses to climate change due to the pervasive lack of comprehensive carbon-based data at the whole-stand level. We employed an integrated approach combining micrometeorological techniques (Eddy Covariance, EC), process-based and biogeochemical modelling, tree ring width (TRW), and quantitative wood anatomy to assess changes in carbon fluxes and allocation dynamics over mature stands of black spruce (Picea mariana Mill.) and jack pine (Pinus banksiana Lamb.) from 1999 to 2021 in Canada. We used Gross Primary Production (GPP) from EC to calibrate and validate GPP simulations from the 3D-CMCC-FEM model, incorporating tree ring width (TRW) and wood anatomical traits, such as cell wall area (CWA), as proxies for carbon fixation.