Tree carbon allocation dynamics determined using a carbon mass balance approach

Summary Tree internal carbon ( C ) fluxes between compound and compartment pools are difficult to measure directly. Here we used a C mass balance approach to decipher these fluxes and provide a full description of tree C allocation dynamics. We collected independent measurements of tree C sinks, source and pools in P inus halepensis in a semi‐arid forest, and converted all fluxes to g C per tree d −1 . Using this data set, a process flowchart was created to describe and quantify the tree C allocation on diurnal to annual time‐scales. The annual C source of 24.5 kg C per tree yr −1 was balanced by C sinks of 23.5 kg C per tree yr −1 , which partitioned into 70%, 17% and 13% between respiration, growth, and litter (plus export to soil), respectively. Large imbalances (up to 57 g C per tree d −1 ) were observed as C excess during the wet season, and as C deficit during the dry season. Concurrent changes in C reserves (starch) were sufficient to buffer these transient C imbalances. The C pool dynamics calculated using the flowchart were in general agreement with the observed pool sizes, providing confidence regarding our estimations of the timing, magnitude, and direction of the internal C fluxes.