Xylogenesis under climatic stress: wood anatomical evidence of harsh conditions

Xylogenesis – the process of secondary xylem formation – is tightly regulated by hormonal, physiological, and environmental signals, but becomes highly vulnerable under extreme climatic stress. Drought, heatwaves, and late frosts can disrupt key stages of cambial activity, cell production, differentiation, and maturation, leading to the formation of distinct anatomical anomalies in the wood of individual tree rings. We present examples of wood anatomical features collected during xylogenesis experiments in (1) Mediterranean and semi-arid, (2) arid and semi-arid, as well as (3) cold and arctic biomes. The most typical features of Mediterranean and semi-arid biomes – L-type IADFs showing xylogenetic plasticity – are shown in Pinus pinea, Arbutus unedo and Quercus ilex. Drought-induced disruptions of xylogenesis in arid and semi-arid biomes are illustrated by E-IADFs in Arbutus unedo and dark rings in Pinus halepensis. Finally, frost rings in Rhododendron myrtifolium and blue rings in Pinus sylvestris are presented as typical wood anatomy anomalies that occur due to disrupted cambial production and cell differentiation at the beginning or the end of vegetation period in the harsh conditions of cold arctic biomes.