Linking carbon fluxes, tree-rings, and xylem anatomy to better understand the processes of carbon allocation to aboveground woody biomass under drought conditions

Carbon allocation to woody tissues is a key set of processes underlying biomass increment during a tree’s growing season. Existing research has rarely addressed this process from a long-term perspective and its interannual to decadal dynamics remain poorly constrained. This also limits our understanding of the sub-seasonal connections and dynamics between carbon uptake and stem growth under a warming climate. To address this knowledge gap, we collected wood cores from two of the longest existing eddy-covariance records at European beech forest sites in Denmark (Sorø, DK-Sor) and Germany (Hainich, DE-Hai). In my presentation, I will scrutinize the interannual dynamics of aboveground carbon allocation during and following drought extremes by linking carbon flux-based GPP and tree-ring-based aboveground biomass increment. Second, I will assess the different seasonal patterns of carbon allocation on time scales ranging from weeks to months to verify whether growth is indeed prioritized during favorable conditions or de-prioritized when water becomes limiting. Finally, I will talk about future perspectives on carbon isotopes to assess how carbon allocation may change along the stem axis at the individual tree level. Together, these observations help establish a linkage between the seasonal dynamics of carbon and tree physiological processes.