Regeneration of Scots pine stem after wounding

Abstract

Stem regeneration after wounding was studied in 110-year-old trees of Pinus sylvestris L. over a period of 30 years. The changes of cambial surface are shown as 3D models. For construction of the models ArcGIS and geodesic Surfer programs were applied. The trees responded to stem injury by increasing the cambial activity near the wound edge. The result was longitudinal rolls or spindles which gradually covered the wounded stem surface. The successively formed tree rings changed their orientation to perpendicular with respect to the wound surface. The disturbances of wood formation near the wound edge were manifested by oblique orientation of xylem rays with respect to annual ring boundaries. The spatial distribution of the xylem ray orientation is presented on the Surfer contour maps. Near the fusion of the wound spindles there were some areas consisting of irregularly oriented xylem cells. The cellular ordering of the xylem tissue in these areas was measured by applying digital image analysis software. Measurements shown on color-coded maps revealed that the tracheid orientation (seen on tangential sections) deviated between 0 and 90 degrees from the stem axis. In some areas a circular pattern of tracheid orientation was visible. Crooked and forked tracheids were also present. These results support the view that the adaptive growth occurring in the case of deep wounding is analogous to that observed when an inanimate body is in lateral contact with a tree stem. The intensive growth and accumulation of newly deposited tissue in the wound spindles seems to be the most effective mechanism for the tree stem regeneration to restore its biomechanical and transport functions. This could be considered as an illustration of Wolff’s law that the shape of an organ follows its function.

Xylogenesis in response to severe traumatism in the Canary Island pine (Pinus canariensis C. Sm. ex DC)

“…Xylem development via centripetal divisions forces the cambium to recover its normal position, parallel to the organ surface (Figure 5). This first traumatic xylem shows a high proportion of resin ducts, axial parenchyma, and irregular shaped tracheids, as already described for other species (e.g Oven and Torelli 1999, Zajaczkowska 2014a, Arbellay et al 2014…”

“…In these regions, also tangential resin ducts are developed, perpendicular both to axial and radial canals. Malformation and disorganization of tracheids in woundwood, as well as the later recovery of a normal pattern has been recently described in beetle and fire scars in different conifers (Arbellay et al 2014(Arbellay et al , 2017 or in mechanical injuries in the stem of Pinus sylvestris (Zajaczkowska 2014a) or even in overgrown stumps of felled Pseudotsuga menziensii (Zajaczkowska 2014b).…”

“…Traumatic wood usually presents malformed tracheary elements and fibers, with altered lignification patterns, and with a high proportion of parenchymatic cells. Orientation of these elements is also very often distorted (Zajaczkowska 2014a, 2014b, Arbellay et al 2014, Chano et al 2015, probably due to altered hormonal flux, and also to altered mechanical signals, as suggested in Chapter 2 (Chano et al 2015). This disorganized xylem implies an evident disadvantage for water and nutrient transport (Arbellay et al 2014).…”

“…Our results show that healing of fenestration wounds in P. canariensis progresses exclusively from the lateral margins, via proliferation of vascular cambium cells, which is perceptible 2-4 weeks after wounding. The cambium twists inwards, heading the surface of the wound, probably due to a very high number of multiplicative, radial anticlinal divisions, which generate additional cambial cells, as discussed byZajaczkowska (2014a) in P. sylvestris. The proportion of radial anticlinal divisions is related negatively with the distance to the healing border, i.e., they are more frequent near the border, and ultimately would lead to the reconstruction of the cambial circumference.Simultaneously, first periclinal divisions give rise to parenchymatous cells outwards, which form a protecting callus.…”

“…or in mechanical injuries in the stem of Pinus sylvestris(Zajaczkowska 2014a), or even in overgrown stumps of felled Pseudotsuga menziensii(Zajaczkowska 2014b). This disorganized xylem, with an increased proportion of resin ducts and associated parenchyma imply an evident disadvantage for the circulation of water and nutrients through the traumatic xylem(Arbellay et al 2014).…”