Constitutive resin ducts formation in Pinus sylvestris responds to water availability and temperature in southern Siberia

Abstract

Constitutive resin ducts (RDs) are a distinctive anatomical trait in the xylem of most conifers, playing a clear defensive role against biotic and abiotic factors. Although resin duct dynamics are well documented in Mediterranean environments, less attention has been dedicated to continental climate. In this study, we evaluated the occurrence and climate response of resin ducts in Pinus sylvestris L. trees in five sites along a 3422 km transect of increasing continentality in the forest-steppe of southern Siberia over the 1966–2016 period. Our results suggest a strong climatic dependence of tree growth and resin duct production under the Siberian continental climate conditions. Tree-ring width and RDs abundance were positively affected by summer precipitation and negatively influenced by temperature and solar radiation, suggesting a link between RDs formation and the water deficit period that limits RW. However, the RDs climate signal was generally weaker, with the strongest climate response occurring later in the season, showing independent signals when the RW effect was removed. The site played a key role as an explanatory factor of the climate response variability. Although no clear pattern was found along the transect, potential differences are due to phenotypic variations between the P. sylvestris populations. Warming-induced drought conditions during the growing season, associated to ongoing climate warming, might affect tree growth and resin ducts production with an increase of this critical defensive structure abundance in conifers growing in the forest-steppe in southern Siberia.