Influence of Temperature on Cambial Activity and Cell Differentiation in Quercus Sessiliflora and Acer Pseudoplatanus of Different Ages

We evaluated the response of active cambium of sessile oak (Quercus sessiliflora) and sycamore maple (Acer pseudoplatanus) to experimentally increased (20–22 °C) and decreased (9–11 °C) temperatures. Heating and cooling experiments on 150-year old Q. sessiliflora were performed during the growth season of 2007 and on 30-year old A. pseudoplatanus in 2008. In 2009, heating experiment was carried out on 30-year old Q. sessiliflora. For each treatment, two trees were selected of each species and sampled at 21-day intervals during the vegetation period and investigated by means of light microscopy. Continuously elevated temperatures slightly promoted the development of xylem cells in old Q. sessiliflora trees in the first month of cambial activity. However, no effect of elevated or decreased temperature was detected in the timing and dynamics of wood and phloem formation. The applied treatments, therefore, had no visible impact on the structure or width of the xylem or phloem increments in 2007. On the other hand, heating young A. pseudoplatanus trees provoked the development of epicormic shoots two months after the onset of the experiment and finally the death of trees. The cambium of those trees did not reactivate in 2008; xylem and phloem increments were consequently not formed. Low temperature treatments slowed down cell production at the very beginning of the growing season, but no alterations in wood or phloem formation dynamics or structure were observed later. The heating of young Q. sessiliflora trees caused the development of epicormic shoots and the death of trees four months after the experiment. The pattern of their dying was similar as in A. pseudoplatanus but with a two month delay. The observations indicate that tree age, thickness of dead bark and duration of the applied treatments influence the response of cambium. The development of dead bark is species specific and it occurs earlier in Q. sessiliflora than in A. pseudoplatanus. Thick dead bark acts as a very good insulation layer for the sensitive internal, living tissues of bark and cambium and therefore protects them against external abiotic and biotic factors.