Carbon uptake, storage, and allocation patterns contribute to blurring of annual ¹⁴C 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.