Canopy status modulates formation of wood rays in scots pine under hemiboreal conditions

Non-structural carbohydrates (NSC) reserves are crucial for trees to cope with weather extremes, thus to ensure their survival and ecological plasticity. The NSC reserves can depend on social status, suggesting uneven plasticity of trees at the stand level. In stemwood of Scots pine (Pinus sylvestris L.), which is a widespread and important species, NSC reserves are stored in parenchyma in wood rays (WR). The quantity of WRs is adjusted intra-annually, allowing retrospective analysis of factors affecting their formation. Accordingly, the differences in WR quantity in stemwood of dominant and intermediate (canopy trees with reduced and narrow crowns) maturing Scots pine were assessed by quantitative wood anatomy. Tangential cuts from the outermost 30 tree-rings were analysed. The relative ray area was intermediate, i.e. covering about 5% of the tangential cut, yet expressed high individuality among the trees. The size and amount of WR mainly differed between the earlywood and latewood; WRs in latewood were higher although narrower in comparison to earlywood, yet their total amount was higher in earlywood. Canopy status had only a slight effect, as quantity and height of WR tended to be higher for the intermediate trees, particularly in earlywood. The size and quantity of WR expressed inter-annual variation, which was mainly related to the meteorological conditions prior to the formation of the tree-ring (previous summer and autumn) indicating legacy effects of climatic factors on NSC and susceptibility of trees to cumulative effects of weather extremes. However, the climatic signals in the inter-annual variation of WR were weaker than observed before, likely due to location of the studied stand in the mid-part of the species range. Nevertheless, the observed differences in mean values and inter-annual variation of WR suggested a within-species diversity of carbon allocation patterns, supporting adaptability of the species.