Survival of temperate‐zone tree species under the normal summer‐winter cycle is dependent on proper timing of apical growth cessation and cold acclimatization. This timing is primarily based on the perception of daylength, and through evolution many tree species have developed photoperiodic ecotypes which are closely adapted to the local light conditions. The longest photoperiod inducing growth cessation, the critical photoperiod, is inherited as a quantitative character. The phytochrome pigment family is the probable receptor of daylength, but the exact role of phytochrome and the physiological basis for the different responses between photoperiodic ecotypes are not known. This report shows for the first time that over‐expression of the oat phytochrome A gene (PHYA) in a tree significantly changes the critical daylength and effectively prevents cold acclimatization. While the critical daylength for elongation growth in the wild‐type of hybrid aspen (Populus tremula × tremuloides) was approximately 15 h, transgenic lines with a strong expression of the oat PHYA gene did not stop growing even under a photoperiod of 6 h. Quantitative analysis of gibberellins (GA) as well as indole‐3‐acetic acid (IAA) revealed that levels of these were not down‐regulated under short days in the transgenic plants expressing high levels of oat PHYA, as in the wild‐type. These results indicate that photoperiodic responses in trees might be regulated by the amount of PHYA gene expressed in the plants, and that the amount of phytochrome A (phyA) affects the metabolism of GAs and IAA.
Detailed knowledge of temperature effects on the timing of dormancy development and bud burst will help evaluate the impacts of climate change on forest trees. We tested the effects of temperature applied during short-day treatment, duration of short-day treatment, duration of chilling and light regime applied during forcing on the timing of bud burst in 1- and 2-year-old seedlings of nine provenances of Norway spruce (Picea abies (L.) Karst.). High temperature during dormancy induction, little or no chilling and low temperature during forcing all delayed dormancy release but did not prevent bud burst or growth onset provided the seedlings were forced under long-day conditions. Without chilling, bud burst occurred in about 20% of seedlings kept in short days at 12 degrees C, indicating that young Norway spruce seedlings do not exhibit true bud dormancy. Chilling hastened bud burst and removed the long photoperiod requirement, but the effect of high temperature applied during dormancy induction was observed even after prolonged chilling. Extension of the short-day treatment from 4 to 8 or 12 weeks hastened bud burst. The effect of treatments applied during dormancy development was larger than that of provenance; in some cases no provenance effect was detected, but in 1-year-old seedlings, time to bud burst decreased linearly with increasing latitude of origin. Differences among provenances were complicated by different responses of some origins to light conditions under long-day forcing. In conclusion, timing of bud burst in Norway spruce seedlings is significantly affected by temperature during bud set, and these effects are modified by chilling and environmental conditions during forcing.
Summary• The aim was to elucidate the effects of elevated winter temperatures on the dehardening process of mountain birch ( Betula pubescens ssp. czerepanovii ) ecotypes and to evaluate their susceptibility to frost damage under warming climate conditions.• Ecotypes from 60 to 71 ° N latitudes and 20 -750 m altitudes were grown in northern Norway (70 ° N) and subjected to simulation of the photoperiod in southern Norway (60 ° N) by artificial illumination from September onwards. In November, the seedlings were transported to the south (60 ° N) to overwinter at ambient or 4 ° C above ambient temperatures. Frost hardiness and lipid peroxidation were determined during January-April.• The higher winter temperature accelerated dehardening, and there were significant differences between the ecotypes. Among tree individuals of southern origin, the alpine ecotype exhibited the most rapid rate of dehardening, whereas the oceanic type showed the slowest rate. Lipid peroxidation supported the above findings.• Since temperature elevation was unequal for the ecotypes with respect to climatic change, the frost hardiness results were normalized to obtain an equal +4 ° C temperature rise. The risk of frost injury seemed to be lowest in the northernmost ecotypes under a temperature elevation of +4 ° C, obviously due to their adaptation to a wider temperature range.
Stress adaptations often include a trade‐off of weakened performance in nonlocal conditions, resulting in divergent selection, and potentially, genetic differentiation and evolutionary adaptation. Results of a two‐phase (greenhouse and field) common garden experiment demonstrated adaptation of mountain birch (Betula pubescens subsp. czerepanovii) populations from industrially polluted areas of the Kola Peninsula, north‐western Russia, to heavy metals (HM), whereas no adaptations to wind or drought stress were detected in populations from wind‐exposed sites. HM‐adapted seedlings were maladapted to drought but less palatable (co‐resistant) to insect herbivores, even under background HM concentrations. The absence of adaptations to harsh microclimate and the generally high adaptive potential of mountain birch, a critical forest forming tree in subarctic Europe, need to be accounted for in models predicting consequences of human‐driven environmental changes, including the projected climate change.
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