First record of blue ring in a dicotyledonous angiosperm wood

Key messageWe report the occurrence of blue rings in a dicotyledonous angiosperm wood and show the differences between blue rings and tension wood.AbstractIn plant stems, local and short-term climatic factors highly influence programmed wood cell production, size, shape, wall composition and thickness. Previous analyses of conifer woods have highlighted the formation of a continuous layer of less lignified axial tracheids, the so-called blue ring. Until now, blue rings have never been described in dicotyledonous angiosperm woods. Here, we report the formation of blue rings on two Populus x canadensis clones ("Tucano" and "San Martino"), and we discuss potential causal factors related to environmental growing conditions, wood formation, and plant hormones. Blue rings were observed in all 13 poplar cuttings included in the study, with the primary driving factor identified as a lack of hormonal signalling due to apical bud and young leaf damage after intense warmth. Our analyses emphasised the strong influence of short-term events on blue ring formation, the interconnection between lignification and leaf-originating signals, and a clone-specific response to apical bud and leaf damage. Identifying blue rings in angiosperms could promote studies on plant adaptation to a changing climate and refine paleoclimate reconstructions from tree rings.