Carbon uptake, storage, and allocation patterns contribute to blurring of annual 14 C signals in tree rings

Tree rings are considered the gold standard for observing variation in past atmospheric radiocarbon (14C), yet little attention has been paid to whether different trees record tropospheric 14C evenly. The discovery of Miyake events, rapid increases in 14C production occurring in past millennia, has led to repeated measurements of 14C in tree rings across species and locations. These records demonstrate remarkable synchrony, yet significant variability between samples remains, limiting reliable use of tree rings as a precise indicator of the timing and scale of past 14C production. Understanding how trees and species record tropospheric 14C would improve reconstructions of past 14C production events, refine geochronological control, and because of the pulse-like nature of past 14C production events, shed light on a fundamental question in tree physiology and dendrochronology: what is the lag time between photosynthesis, storage, and allocation to wood and how might this lag blur isotopic signals in tree rings? Here, we evaluate the implicit assumption that all trees record tropospheric 14C evenly by focusing on the path carbon takes within trees including: phenology of carbon uptake and wood formation, storage and use of nonstructural carbohydrates, and how these factors interact to affect the tropospheric 14C signal in wood.