Spatiotemporal variability of xylem trait response to climate of a high-elevation conifer species across its geographical range

Understanding spatiotemporal responses of plants to climate variability is crucial when predicting future scenarios. This is especially urgent for relict species growing in heat-limited ecotones, as biodiversity spots facing faster warming than the global average. Long-term climate sensitivity of woody species has been extensively investigated through tree-ring width analysis, while only recently studies examined wood-anatomical traits. Yet, no one considered the species responses across its entire geographical distribution. We explored climate sensitivity of Pinus cembra, a high-elevation relict species endemic to Alps and Carpathians, across its entire distributional range analysing its xylem anatomical traits over 6 sites. Climate-growth associations for mean lumen area, cell wall thickness and cell number have been computed using temperature and precipitation daily climate records from 1920 to 2010. Series were aligned to the growing degree days, accounting for their inter-annual variability and the associated varying xylogenesis dynamics. Anatomical chronologies featured common variability within the two mountain ranges, while were distinct between the two areas and likely associated to regional climate modes. Nonetheless, the pattern in the climate-anatomical traits associations suggest a unique species-specific mechanism of response with cell number and cell wall thickness positively related to temperatures and negatively to precipitation and lumen area showing the opposite. In the last 30 years, we observed a slight advance of the growing season, especially in the Alps, and a decrease in the climate sensitivity, suggesting a relaxation of the limiting conditions. With climate warming, we may expect an increased in radial growth and associated xylem hydraulic adjustments.