During the growing season, the cambium of conifer trees produces successive rows of xylem cells, known as tracheids. Current knowledge on this process mainly stems from xylogenesis monitoring spanning a few years.
In this investigation of the effects of long-term inter-annual climate variability on tracheid formation and wall thickening, Castagneri et al. retrospectively study tree-ring xylem anatomy in Picea abies along an altitudinal gradient in the Alps. Climate fluctuations are shown to influence morphogenesis of tracheids sequentially formed in the growing season over successive periods. Morphogenetic mechanisms responsible for different tracheid traits are affected by climate to differing degrees according to the extent of elevation. This long-term high-resolution analysis of xylem anatomy could support short-term xylogenesis observations, offering insights into the ways in which climate controls tree growth and functioning.