Current issue: 54(2)
The relationships between bud dormancy and frost hardiness were examined using two-year-old Pinus sylvestris L. seedlings. The chilling temperatures used were +4 and -2°C. To examine the dormancy release of the seedlings, a forcing technique was used. Frost hardiness was determined by artificial freezing treatments and measurements of electrical impedance. At the start of the experiment, the frost hardiness of the seedlings was about -25°C. After the rest break, the seedlings kept at +4°C dehardened until after eight weeks their frost hardiness reached -5°C. At the lower chilling temperature (-2°C) the frost hardiness remained at the original level. When moved from +4 to -2°C, seedlings were able to reharden only after the time required for bud burst in the forcing conditions had reached the minimum.
The PDF includes an abstract in Finnish
The premises of several models obtained from literature on bud dormancy release in trees from cool and temperate regions differs from each other with respect to responses to air temperature during the rest period of the buds. The predicted timing of bud burst in natural conditions varied among the models, as did the prediction of the models for the outcome of a chilling experiment.
Experimental results with two-year old seedlings of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) H. Karst.) did not agree with any of the models. The experimental results also deviated from abundand earlier findings, which also disagreed with any of the models. This finding suggests that Finnish provenances of Scots pine and Norway spruce differ from more southern provenances with respect to temperature regulation of bud dormancy release.
A synthesis model for the effects of air temperature on bud dormancy release in trees was developed on the basis of the previous models and the experimental results of both the present and previous studies. The synthesis model contains part of the original models as special cases. The parameters of the synthesis model represent several aspects of the bud dormancy release of trees that should be addressed separately with each species and provenance in experimental studies. Further aspects of dormancy release were discussed, in order to facilitate further development of the models.
The PDF includes a summary in Finnish.